What is the difference between log in, sign in; register, sign up; log out, sign out [duplicate]

Question

Although they are all over the Internet, but the answers are not fixed and were not asked all 4s at a time causing me to be confused.

Is it accurate if I say:

• both login and sign in are the same as authenticate
  verb, to validate the user. Otherwise password are not required.
• both logout and sign out are the same
• log in is to authenticate into a website that has different interface as guest
  You cannot use the logged in interface if you are a guest, e.g. Facebook
• sign in is to authenticate into a website that has same interface as guest
  You can still use the website without signing in, e.g. Google
• register is entering your information into the system for your account for serious thing
  You need to enter your information like name, address, contact number, etc for domain registration. Another example is company registration.
• sign up is to create an account to use
  You only need to enter essential information like email, username, password, etc for a Facebook account.

Answer 1

There are several different groups of words here.

log in, sign in, login, log on, logon, authenticate

All of these words are more-or-less synonyms. "Login"/"logon" may or may not be acceptable (check your style guide). If they are, they may be nouns instead of verbs (referring to the action of logging in or the state of being logged in).

There is no widely-understood difference between any of these words except as described above.

"Authorize" is not on this list. In computer security, authorization and authentication are not the same thing. The items on this list are all authentication. Authorization refers to deciding what someone is permitted to do after you've established their identity (e.g. on Stack Exchange, moderators are authorized to do various things which the rest of us are not).

log out, sign out, logout, log off, logoff

Likewise, these words are synonyms. As above, "logout"/"logoff" may not be OK. Also as above, there is not much meaningful difference between them. Some of the words in this list do correspond to some of the words in the previous list, so you should probably choose your words to match each other.

register, sign up

These are synonyms, but they both refer more broadly to providing information in order to receive some service or to be placed on some list. For instance, you might sign up or register for a loyalty program at your grocery store. You could even sign up to join the military.