A "bootleg" or "edit" in DJ context is an unofficial remix or rework of an existing track, made by a DJ for use in their own sets.

What they are

A DJ takes a famous track (often from outside DnB), reworks the structure or tempo to fit DnB, and plays it in their set. The result is usually not legally distributable because the original sample was not cleared. But the DJ can play it.

Why DJs make them

Bootlegs create unique set moments. Hearing a known pop or rock track suddenly appear at 174 BPM in a DnB set is the kind of moment that makes the night memorable. Most working DnB DJs have a small collection of personal bootlegs they reserve for the right moments.