what does the term  ep refer to?
An extended play, often referred to as an EP, is a musical recording that contains more tracks than a single but is usually unqualified as an album or LP.
Extended play
An extended play, often referred to as an EP, is a musical recording that contains more tracks than a single but is usually unqualified as an album or LP. 
who sang tik tok and we are who we are Kesha. does it belong to any album? No, its from her extended play (EP), "Cannibal".
wiki:5243993
Extended play [SEP] Introduction
An extended play, often referred to as an EP, is a musical recording that contains more tracks than a single but is usually unqualified as an album or LP. Contemporary EPs generally contain a minimum of three tracks and maximum of six tracks, and are considered "less expensive and time-consuming" for an artist to produce than an album. An EP originally referred to specific types of vinyl records other than 78 rpm standard play (SP) and LP, but it is now applied to mid-length CDs and downloads as well. Ricardo Baca of "The Denver Post" said, "EPs—originally extended-play 'single' releases that are shorter than traditional albums—have long been popular with punk and indie bands." In the United Kingdom, the Official Chart Company defines a boundary between EP and album classification at 25 minutes of maximum length and no more than four tracks (not counting alternative versions of featured songs, if present).