-- "You should check out the new bootleg then, I'll send you the link!"
A bootleg recording is a audio or video recording of a performance that was not officially released by the artist or under other legal authority. A great many such recordings are simply copied and traded among fans of the artist without financial exchange, but some bootleggers are able to sell these rarities for profit, sometimes by adding professional-quality sound engineering and packaging to the raw material.
This term originated with smugglers and thieves who would hide things in the leg of their boots. It evolved to mean a pirated version of something. Some liberal bands such as the Grateful Dead, and more recently Phish and Pearl Jam allow fans to record their concerts, and distibute these recordings freely as long as they are not sold. Fans refer to such recordings as "bootlegs", even though they are legal.