EP

An extended-play record, for whatever that meant. Usually it meant more than one cut on at least one side. Some EP's were issued in 7-inch size but played at 33 RPM.

Also refers to the extended-play speed for VHS, allowing six hours of video recording on a standard-sized videocassette, at the cost of lower resolution than SP speed and faster degradation of quality over time.

Also known as SLP.

Even in the current age, a CD may be referred to as EP (extended play) if it has a few too many tracks to be a single, but not enough tracks to be an LP. EP's are typically released by independent bands because they don't have enough money to record a whole album's worth of material. An EP might have 5 or 6 tracks on it, and a total of 20 minutes of music on it. Appearance-wise, it looks like a normal CD.

Some people refer to CD singles as EPs as well. It's really a question of taste. Personally, I prefer to call those shorter, "single-length" recordings EPs only if they lack a defining track.

For instance, the Chemical Brothers' "Loops of Fury EP" is the only release to contain the letters EP in its title. The case is also made of white plastic instead of the usual black. This qualifies as an EP because all 4 tracks are different (read, not remixes of each other). Indeed, this release does not identify with any one album. You see, two of the tracks, Loops of Fury and These Beats Were Made For Breakin', appear on no album. Differing mixes of the other two tracks, "Chemical Beats (Dave Clarke Remix)" and the full version of "Get Up On It Like This", appear on two different albums, respectively Exit Planet Dust and Dig Your Own Hole.

EP is short for "extended play". That means it's longer than a single (shorter than 10 minutes) but shorter than an album (longer than 30 minutes). EPs usually also have a title, as opposed to singles which are named after the first track. It isn't quite as simple as that, however. A recording longer than 30 minutes may be considered an EP, if only alternative versions of songs, remixes or anything like that is the only thing making it over 30 minutes long. And nowadays it's more about that the artist decides that it's an EP, and I recall at least one EP with less than 10 minutes of material. This also excludes singles with a bunch of remixes from being EPs.

BQ09

EPs are often, but not always, a piece of their own, especially after the disappearance of the mini-LP due to the CD-age. This means that you might not find any of the EP's tracks on albums, like you would with a single. A famous example is Nine Inch Nails' Broken* EP, which is as considered as important as a full album in their discography. EPs were especially important to punk and other independant DIY-genres. Punk (especially hardcore) songs, as you might know, are quite quick, and you have to have more of them than "normal" songs in order to fill an album. And not only were EPs therefore easier to fill, but also cheaper to manufacture.

* Broken actually clocks in just over thirty minutes, but ten of those are two hidden tracks which are at a long distance (both by silence and their content) of the other tracks.