'Corkscrew'. This is a decoration usually done by a leader. The classic version of the enrosque is where he leads his partner to do a giro around him, and he holds back on his own turn for a moment before spinning sharply on his standing foot while quickly hooking the other around it. The double turning movement creates a kind of ooptical illusion of extreme spin.
Another common way to do an enrosque is this: if you're standing on, say, your left leg and turning clockwise, then you let your right foot trail on the floor so that your right leg becomes wrapped around your left as a result of the turn.
Ultimately, though, an enrosque is any step where you're turning and wrapping your free leg around the other in a way which looks like a corkscrew. There are a million places you can throw in an enrosque. Here are some examples:
Enrosques can also be done by followers, but it's not so common. Where a leader might do an enrosque, a follower is more likely to do a variation of the rulo where she draws a small circle on the floor while pivoting. See the rulo page for a video of this.
This video starts off with standard enrosques, and moves on to the follower's fancy rulo.