An album is a collection of audio recordings released as a single item on a CD, vinyl, audio tape, or digital distribution. Early albums were multiple 78 rpm records in a bound book resembling a photo album. The term "album" was first used in musical contexts in the early 19th century, for collections of short printed pieces of music. In the early 1900s, 78 rpm records could hold only about three minutes of sound per side, which led to almost all popular recordings being limited to around three minutes in length.