EP stands for "extended play." LP is short for "long play," or "long player."
EP and LP distinctions originally referred exclusively to vinyl records, but the terms carried through to the cassette-tape format and remain in use today for compact discs and digital downloads.
While LPs are full-length albums, generally 25 minutes or longer, EPs contain three to five songs and are shorter than 25 minutes.
The full-length LP and the single, containing one or two songs, were the primary promotional formats in popular music prior to the advent of EPs in the 1970s and 1980s. EPs allowed record companies to send radio stations a more comprehensive introduction to a new band or preview live albums by established acts.
LPs developed into expanded formats, such as double- and triple sets. EPs evolved to included the "split," or tracks from multiple bands on the same record label.