As a noun, bootleg means the top part of a boot, the part that is around the leg instead of the foot. From the practice of hiding small items in a boot to smuggle them past the authorities, the word became a verb, meaning "to smuggle", and an adjective, describing something that has been smuggled (or, more rarely, stolen). Anything that is regulated can be bootlegged, so the term now often refers to such items as audio or video recordings not released by whoever holds the rights to them (also known as "pirated" copies)
http://en.wikipedia.org/wiki/Bootleg