What is the difference between "up in here" and "in here"? And what does "up in here" mean?

Question

A friend of mine from London tried to explain the difference to me, but still I got no definite answer. He said "It's one thing," but "up in here" has... something... special—anyway I don't know.

Answer 1

Echoing what bye said in their comment, "Up in here" is AAVE or African-American Vernacular English, which has its own rules and grammar that are distinct from other American English dialects.

As a phrase, "up in here" simply refers to a something/somewhere that is well-known to the speaker or about which the speaker is knowledgeable.

OSD definition: Used to refer to a location (close to the speaker, or where the speaker currently is) with which one is familiar, or where one lives.

The most obvious use of this phrase is in DMX's "Party Up (Up in Here)", where he's referring to the rap game as the "up in here" place he's familiar with and the new/upcoming rappers as the "y'all" making him lose his mind.

I'd say that "in here" by itself is used more for only specifying the current location of a speaker.

E.g.   A: "It's cold." B: "Where's it cold?" A: "It's cold in here."

Answer 2

I found this site because I wondered about "up in here" and I can tell you that it has moved beyond AAVE because I hear white people in North Carolina say it all the time.

Answer 3

Reference-work definitions of 'up in here' and related expressions

A walk through Urban Dictionary's page on "up in here" finds entries for the expression from as early as 2003, and the earliest definitions offered are straightforward and seemingly independent of any adjacent wording. From April 4, 2003, Action Squirrel offers this definition:

here, in this vicinity, at this present location

And from October 8, 2003, Willy offers this one:

in this place

The meaning thus seems extremely similar to "in here" or simply "here" in reference to a place or location.

The Online Slang Dictionary page for "up in here" offers a similar definition:

at the current location.

and cites an occurrence of the phrase in Scary Movie 3 (2003).

As it turns out, there are also instances of the expression in the first Scary Movie (2000), spoken by Regina Hall's character Brenda:

Old Man: [annoyed] Excuse me?

Brenda: Uh ha... I think I paid my money like er'ybody else up in here!

[Watching the movie]

Brenda: That ain't no man! You can see her real hair right there!

Young Lady: [turning around] Do you mind?

Brenda: [sticking out her hand to the women's face] I know you better get outta my face! Outta my face! Outta my face! This is all me up in here! You handle 'dat!

Significantly later Urban Dictionary entries, identify narrower or more particular meanings that arise when "up in here" appears as part of a longer idiomatic phrase. Thus, for example, a July 2, 2009 entry submitted by kofyslug addresses the phrase "got any cherries up in here":

Said when looking for something fresh in a stale place. [Example:] Dude, this party sucks. They got any cherries up in here?

A February 10, 2012 entry from Fireball BD offers a definition of "gettin' squirrely up in here":

A phrase used to describe a situation that is totally out of hand or ridiculous.

A March 6, 2012, entry from Rick Pick offers this definition for "all up in here":

It means that a person is being obnoxious or otherwise unpleasant. To annoy someone to an extent. [Example:] Dude, get out of my face... your all up in here!

And a June 23, 2017, entry submitted by hoodscro asserts that "come up in here" means "steal [things]";

Posting to Urban Dictionary on October 28, 2010, Sandra21 discusses the meaning of the similar phrase "up in this here":

Variation of 'up in this piece', 'in this place', 'in here'

Randy Kearse, Street Talk: Da Official Guide to Hip-Hop & Urban Slanguage (2006) doesn't have an entry for "up in here" but it does include several phrases that begin with "up in":

{to be} up in {a female} (sexual sl[ang]) new school | a term males use for having sex. (var. {to} go up in {a female}

{to be} up in {someone's} business phrase (general sl[ang]) old & new school | to be in someone's personal affairs for the sole purpose of being nosy (var. {to be} all up in {someone's} business)

{to be} up in {someone's} spot phrase (general sl[ang]) new school | the act of visiting someone's dwellings or place of business.

up in this piece phrase (general sl[ang]) phrase (general sl[ang]) old & new school | a hip way of saying "in here" when referring to one's immediate location. (var. up in this bit[ch])

This last entry tends to support Sandra21's association of "up in this piece" with "[up] in [this] here." It seems that an array of variant forms of "up in here"—including "up in this piece," "up in this bitch," and "up in this here" existed within a few years of 2003, when Urban Dictionary first showed awareness of the term. For the record, Urban Dictionary's earliest entry for "up in this piece" is from 2006.

A notable earlier occurrence of "up in here" (also cited in afry's answer and in JPhi1618's comment) is in the 1999 rap song "Party (Up in Here)" by DMX [Earl Simmons], where the phrase occurs repeatedly in what amounts to the refrain of the piece:

Y'all gon' make me lose my mind / Up in here, up in here / Y'all gon' make me go all out / Up in here, up in here

Y'all gon' make me act a fool / Up in here, up in here / Y'all gon' make me lose my cool / Up in here, up in here

Simmons was from Mount Vernon, New York, near New York City.

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Earlier matches for 'up in here' from film dialogue

An Internet Movie Database search for "up in here" in the relevant sense turns up a number of matches from the 1990s and one from the 1980s.

One early occurrence arises in Ted Demme's film Life (1999), in which Eddie Murphy's character Rayford Gibson has the following line:

Rayford Gibson: ... you can't have my cornbread. That's for damn sure. 'Cause if you try and take my cornbread, part 2 of my killing spree is gon' begin up in here on your ass, right now. You thinking about my cornbread, better get the taste out your mouth. That's for damn sure.

Life is set in rural Mississippi, although the lead characters are evidently supposed to be from New York City.

From Don Cheadle's character Maurice "Snoopy" Miller in Steven Soderbrgh's film Out of Sight (1998):

Maurice "Snoopy" Miller: Glenn, I know you are supposed to be cool and everything but you don't got to give me no tone of voice. You don't like what I'm saying, you just bounce the fuck up out of this whip [automobile] anywhere along up in here man.

Miller is supposed to be from Detroit.

From the Chris Rock-voiced character Roger 'Budda' Sack in an episode of Mike Judge's animated TV show King of the Hill (1998):

Roger 'Buddha' Sack: [feigning sadness] You right, you right. Buddha Sack is a sad man. But not as sad as your daddy's sorry self with his four eyes, too-many pies, super size, crackerjack prize... somebody help me out here...

Bobby Hill: And he likes French fries!

Roger 'Buddha' Sack: Ladies and gentlemen, this kid's gonna be the white Rerun! We got the white Rerun up in here!

From Pam Grier's character Jackie Brown, in Quentin Tarantino's film Jackie Brown (1997):

Ordell Robbie: What you care?

Jackie Brown: What I care is my ass facing the penitentiary. If you send some hard-headed rock whore up in here...

Ordell Robbie: Hey, hey, hey, hey. She ain't gonna be no "rock ho." She gonna be cool. Promise.

This movie is set in Los Angeles, California, in 1995.

From John Witherspoon's character Mr. Jones in F. Gary Gray's film Friday (1995):

Mr. Jones: [in toilet] Boy, bring your ass up in here. What you talkin' 'bout, you wait 'til I come out? I smelled your shit for 22 years, now you can smell mine for five minutes.

The setting for Friday is South Central Los Angeles.

In the Hughes brothers film Menace II Society (1993), Clifton Powell's character Chauncy has this line:

Chauncy: Man, get the fuck out of here! Don't bring your narrow ass up in here no more! Go on back to Westwood where you belong!

This film is set in the depressed Watts neighborhood of Los Angeles, within the larger South Central area of the city.

From Janet Hubert's character Vivian Banks in an episode of the TV show The Fresh Prince of Bel-Air (1990):

Policeman: Could you ask your wife to calm down?

Vivian Banks: Calm yourself, Barney Fife.

Phillip Banks: Vivian, please. Now officers, I'm sure we can clear this whole matter up quite easily.

Sergeant: Could you please sit down? We're busy now.

Vivian Banks: [removing earrings] Oh, honey, we're about to get very busy up in here.

The Fresh Prince of Bel-Air was a situation comedy TV show with a largely Black cast, set in the ritzy Bel-Air neighborhood of Los Angeles.

And from Eddie Murphy in Eddie Murphy: Raw (1987):

Eddie Murphy: Hey, don't mind the cameras, everyone. They're filming a movie up in here. And [shouts] y'all gonna be in it! Only I'm the only one gonna get paid, ...

This film consists of footage of a standup comedy performance by Murphy in New York City's Felt Forum at Madison Square Garden. Murphy himself is from Brooklyn, New York, although he has obviously also spent considerable time in Los Angeles.

Interestingly, neither Geneva Smitherman, Black Talk: Words and Phrases from the Hood to the Amen Corner (1994) nor Clarence Major, From Juba to Jive: A Dictionary of African American Slang (1994) has any mention of "up in here" (or "up in" anything else). The three likeliest explanations for their silence on this point are as follows: (1) "up in here" was only regionally current in informal Black English in 1994; (2) the expression was in fairly widespread use, but neither Smitherman nor Major was aware of it; (3) it was in use but was so completely interchangeable with "in here" and "here" that neither Smitherman nor Major considered it distinctive or slangy enough to merit an entry. Each of these possibilities seems plausible.

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Conclusions

Except when it occurs as part of a longer idiomatic phrase—such as "all up in here"—the term "up in here" doesn't seem to carry a substantively different meaning from "in here" or "here." It does, however, appear as one of a family of expressions originating in African American slang that begin with "up in," and it seems probable that it carries a certain cachet that "in here" and "here" do not—even when spoken by people who are not African American.

With regard to the phrase's origin, it seems clearly to have arisen in Black English. The disproportionate number of early instances of the expression from 1997 and earlier that occur in films set in Los Angeles may be a manifestation of the disproportionate number of films set in Los Angeles overall, but it is striking nonetheless. The very earliest match I found was from 1987, in a live performance by Eddie Murphy.