Each subject matter has its own set of terms called jargon which is expressed in its particular grammatical rules. Technical terminology or Term of Art is the specialized vocabulary of any specialized field of knowledge, not just technical fields. So what is the difference between jargon and technical terms?
In his classic book, The Careful Writer, Theodore Bernstein has an entry on inside talk, in which he includes the subclassifications of: argot, jargon, lingo, and slang. He states (p. 237):
The reason that all these words have disparaging connotations is that outsiders dislike being outsiders. They envy or resent those who can speak and understand inside talk. And in some instances the very desire to keep outsiders out accounts for these languages...There is a tendency in specialized groups, for reasons of either establishing a kind of mystic bond or asserting a kind of self-importance, to employ esoteric or pretentious words... This is by no means to say that all inside talk, all jargon, is pretentious and useless. On the contrary, most of it is highly necessary. Those in specialized fields have a need to communicate with one another in precise terms and with an economy of expression. A single word will often convey to a colleague what would require a sentence, a paragraph, or perhaps an even longer description to convey to a layman. The fact that the layman does not comprehend the single word does not indict it for use within its proper sphere...
A final caution may be of value in a discussion of inside talk. In writing intended for general reading, the use, whether by a specialist or by a layman, of jargon terms that are not commonly understood smacks of pedantry. If the writer believes that it is imperative to use such a term, he should at least explain it when it is introduced. It must never be forgotten that the function of writing is communication.
I believe the term jargon has come to mean technical terms used to exclude outsiders to a field. I think you could say that it is the intent of their use that separates jargon from technical terms.
In this definition [M-W], there is no difference; jargon is technical terminology:
3 a : the technical terminology or characteristic idiom of specialists or workers in a particular activity or area of knowledge
In this sub-definition, however, jargon is seen in a derisive light:
often : a pretentious or unnecessarily obscure and esoteric terminology
And the next definition of jargon reinforces this viewpoint:
4 : language vague in meaning and full of circumlocutions and long high-sounding words
As some dictionaries will note, jargon is often used in a way that expresses disapproval or derision. If used in a neutral way, however, jargon simply means technical terminology.
I draw a distinction in that jargon comprises
words and phrases used by particular groups of people that are difficult for other people to understand
— not necessarily the same thing as technical terms, which I associate with officialdom and pedantry.
In other words, jargon is a vocabulary used by people with specialist knowledge, whereas technical term are simply official labels that have been adopted for certain concepts. Both suggest wording that the population at large would find incomprehensible.
Jargon is thus both broader than and more restrictive than technical terminology; it includes words and phrases which may be informal in usage, but by the same token includes words and phrases that cannot be looked up in a manual.
For example, in the pre-merger United Airlines:
Among airline workers and frequent flyer geeks, it was common to refer to the 100,000-status mile/year frequent flyer status as 1K. I would label this as jargon: the 1K desk, the 1K packet, the 1K line.
The official name for that level was Premier Executive 100K. This was the the title on your membership card and how you were referred to in customer service emails (e.g. We welcome your comments as a loyal Premier Executive 100K member), but in practice it was very rarely heard on account of its length and similarity to Premier Executive, the 50,000-mile tier. I would know this as the technical term.
For those unsteeped in the vagaries of mileage programs, either term would have been useless against top tier or 100,000 mile-tier of course.
I want to take a slightly different tack than the previous answers. This is in addition to the other answers, not in contradiction to them.
Technical terms is about nomenclature, and nomenclature can be readily addressed by looking at specialist glossaries. A technical term has a definition, but you you don't need to read a book, or a 16th century paper written in Latin, to understand it's context and usage.
Jargon is a set of terms and usages that often come with historical baggage. It's often about using ordinary terms that have taken on a life of their own ever since some researcher in the 16th century used that word in a specific context. And now that word is reserved for that one specific thing when discussing a particular subject. There is simply no way to grasp the precise meaning other than to have studied the original document or to have been taught the usage in school. A lot of Jargon is a covert reference to specific historical texts and theories. Anyone can talk about circulation, but when it's in the context of aerodynamics, it means Frederick Lanchester's circulation of 1907, later adopted by Prandl, who tried to keep it a secret and thereby drew a great deal of attention to it.
I would also say that jargon may have a looser and more informal meaning; that it may refer to terminology used even just in a particular workplace or between friends, possibly as 'shortcut terminology' rather than technical terminology. I would agree that the term jargon may be used in a derogatory manner, but it doesn't necessarily imply that; nor does it necessarily imply pretentiousness or long-windedness: as I said, it could be a 'shortcut' term.
Etymologically, jargon is “mid-14c., "unintelligible talk, gibberish; chattering, jabbering," from Old French jargon "a chattering" (of birds), also "language, speech," especially "idle talk; thieves' Latin" (12c.). Ultimately of echoic origin (compare Latin garrire "to chatter").
It’s root word jar means: “1520s, "to make a brief, harsh, grating sound," often in reference to bird screeches; the word often is said to be echoic or imitative; compare jargon (n.), jay (n.), garrulous. Figurative sense of "have an unpleasant effect on" is from 1530s; that of "cause to vibrate or shake" is from 1560s. Related: Jarred; jarring. As a noun in this sense from 1540s.”
It wasn’t until the 1650s the term was “"phraseology peculiar to a sect or profession," hence "mode of speech full of unfamiliar terms." Middle English also had it as a verb, jargounen "to chatter" (late 14c.), from French.”
To be true to it’s origins, jargon is a negative term irrespective of how educated or technical words are, but technical, cultural or baby-babble can all be jargon.
All quotes are from Etymonline.com.
Intent is important here. I believe that technical terminology is useful and necessary, whereas jargon's intent is to establish the speaker as an insider, recognizable to other insiders as "one of us". I don't think that it is just a perception from outsiders. I've been involved in too many different industries to ignore insider lingo, as someone who has committed this sin myself. There is definitely an "us" vs. "them" (wink wink, roll of the eyes at how stupid "they" are!) mindset that goes on. And jargon is a huge part of that.