A bootleg recording is one that was not officially released by the artist (or their associated management or production companies). Sometimes they consist of works-in-progress or discarded material distributed against the artist's will; these might be made from master recordings stolen from a studio or label, or from demo recordings not meant to be shared with a wide audience. Bootleg albums can also be recorded "unofficially" with gear smuggled into a live concert—virtually all artists and live venues prohibit such recording, but modern portable technology has made it increasingly easy to do. Some artists, such as Phish, the Grateful Dead, and Dave Matthews Band do allow and encourage live audience recording, but they and their fans generally consider selling such recordings—as opposed to keeping them for one's own personal enjoyment or trading them for other audience recordings—to be bootlegging and illegitimate.

Some artists consider any release for which they do not receive royalties to be a bootleg, even if it is an officially licensed release. This is often the case with artists whose recordings have either become public domain or whose original agreements did not include reissue royalties (which was a common occurrence in the 1950s).

Many bootleg albums have since been released officially by the copyright holder; for instance in 2002 Dave Matthews Band released Busted Stuff in response to the success of the "Lillywhite Sessions" album which they had not intended to release; The Beatles' release of their Anthology albums effectively killed the demand for many Beatles bootlegs previously available; and Bob Dylan has released an entire bootleg series, which as of 2003 had five volumes. Frank Zappa released two series of Beat the Boots recordings in 1991 and 1992, remastered from bootleg tapes.

A few artists like Peter Gabriel and Duran Duran have responded to the demand for bootleg concert recordings by experimenting with selling "official" bootlegs made directly from the live soundboard feed, and thus superior to surreptitious audience recordings which are typically marred by crowd noise and muffled sound; these are generally available a few days to a few weeks after the concert. A newer business model allowed by improving technology in high-speed CD reproduction can make these "official boots" available to audience members as they leave the concert; however, a key patent in the process has been bought by media giant Clear Channel Communications, which appears to be stifling competition and development of the process.

Recently bootlegs have become the term for a style of remix, melding two or more music records into each other to make a new piece of music out of the old components. Among the most popular artists in this genre are The Freelance Hellraiser, Soundhog, Go Home Productions and Lionel Vinyl. These type of records area also referred to as mash ups or bastard pop.

Bootlegging is often incorrectly referred to as piracy but there is an important difference between the two terms. Bootlegging is trading in recordings that the record companies either do not own or are unwilling to release. Piracy is the illegal copying/sale of recordings that are available commercially. Although bootlegging is not legitimate since it invariably violates at least some copyright, it can at least claim it is giving music fans something they want that is unobtainable from official sources. Piracy however cannot make such a moral claim since it purely done for profit rather than filling a consumer niche.

Bootlegging can also refer to the unlicenced filesharing of copyrighted music, but as alluded to above, the term piracy is often more appropriate.