This refers to the old StarTrek when Captain James T. Kirk was in command of the first Enterprise on TV.
The abbreviation amongst fans is "ST:TOS" (The Original Series), followed by ST:TNG (The Next Generation), ST:DS9 (obvious), and ST:VOY.
Do we now also have ST:ENT?
The Star Trek series was originally shown in the late 1960s. Its creator, GeneRoddenberry, intended for it to operate on two levels: as an action-adventure series ("Wagon Train in space"), and also as a forum for exploring social issues.
The prevalent episode pattern is that the Enterprise crew comes across some alien culture with a social problem (racism, religious extremism/intolerance, ignorance, indifference to war or suffering, etc.), and the crew exposes and eliminates the problem by teaching the culture better principles. Sometimes, the crew themselves or the Federation is the culture with the problem, and one of the crew members or an alien being teaches the moral lesson to the others. Often the problems are exaggerated to the point of absurdity for dramatic effect, much like the cultures in Gulliver's Travels. These episodes are allegorical, intended to make viewers think about how the issues are relevant to their own 20th-century Earth.
Another common pattern is that some powerful alien force decides to test humans by presenting them with some sort of puzzle or challenge. The humans always pass the test, generally by exploiting their diversity, freedom of thought and action, goodness, and/or ingenuity.
And there are a few episodes played primarily for laughs, such as "The Trouble With Tribbles".
Some detractors of the show see it as being too preachy and/or absurd.
It is not serious ScienceFiction: the futuristic technologies presented are just a means to tell a story about social issues or to present an idealistic view of humanity in the future.
Some find it ironic that this show that promotes diversity and equality has a 23rd-century government dominated by white American males, and the women all have to wear velvet mini-dresses. Roddenberry's original plan called for 50-50 male/female split and more ethnic diversity, and in the original pilot the women wore the same thing the men did. But the network pressured Roddenberry to change to something that viewers would supposedly find more believable and entertaining.
The series had a small budget, so many of the costumes, props, sets, and special effects are of low quality, and get reused in multiple episodes.
ST:TOS's budget was small only in comparison to current series -- for its time it was not an inexpensive series, althought I don't think it was the most expensive. Reuse/rental was (and actually is) a feature of the tv/movie business in general -- see http://www.westerncostume.com -- ClaudeMuncey
On the gripping hand, StarTrek had a small budget compared to other ScienceFiction series. Other series that aired in the late 60's (Westerns, modern dramas, or sitcoms) relied on a well-established stock of costumes and props; everything in Star Trek had to be created pretty much from scratch. If you were making a Western, it was easy to find period replica guns, but where do you find a phaser? Star Trek needed a higher budget than most other series airing at that time. -- BrentNewhall
Right up until StarWars (IV), SciFi suffered from lopsided budgets. Without a Kubrick on top, putting too much money into the hardware could deprive the writing. (Witness StarWars I-III!)
GeorgeLucas showed the industry - still in shock from the blowout over the DoctorDolittle? merchandizing flop - that elaborate hardware could pay for itself in toy product lines... --PhlIp
Small detail - in the original series they referred to raising "screens" instead of "shields" as is said now when protecting against attack. When did this change on the way to TNG, Voyager etc?
At least some episodes of the original series already refer to shields. I've never heard screens in the later ones.
ST:ENT refers to "Hull Plating"
See GalaxyQuest