I heard this term for the first time today, and realized it is a habit I usually follow rather than firing up a debugger and stepping through my code.
Defined by Dennis Lee Bieber here:
"There's one wolf in Alaska, how do you find it? First build a fence down the middle of the state, wait for the wolf to howl, determine which side of the fence it is on. Repeat process on that side only, until you get to the point where you can see the wolf). In other words; put in a few "print" statements until you find the statement that is failing (then maybe work backwords from the "tracks" to find out where the wolf/bug comes from)."
The original term comes from "The Wolf Fence algorithm for debugging" (Edward J. Gauss, ACM - 1982)