Short answers, pulled from the story.
An extended play (EP) is a musical recording that contains more tracks than a single but fewer than a full album. Contemporary EPs typically contain up to eight tracks with a playing time of 15 to 30 minutes.
RCA Victor introduced the Extended Play 45 in 1952, partly to compete with the long-play record Columbia had launched in 1948. EMI issued the first EPs in Britain in April 1954.
Elvis Presley was RCA's dominant EP artist, with the label issuing 28 EPs between 1956 and 1967. Many of them topped Billboard's dedicated EP chart during its brief existence.
The Beatles released the Magical Mystery Tour film soundtrack as the first double EP in Britain in December 1967, on EMI's Parlophone label. It spread six songs across two 7-inch discs and was packaged with a color booklet.
The Recording Industry Association of America defines an EP as a release under 30 minutes containing three to five songs. This definition is used specifically for certification purposes.
Pop musicians have released EPs to maintain relevance between albums or to deliver an album in installments. Examples include Kesha's Cannibal (2010) following her debut album Animal, and Jessie J's fourth studio album R.O.S.E. (2018) released as four separate EPs on four consecutive days.