I'm helping a neighbour figure some basic stuff out on his Macbook on a regularish basis (I have basically no mac experience, but far more with computers in general than he), and one issue whose solution has eluded me entirely thusfar - apparently, a while back, he accidentally enabled a feature that causes windows to go flying off to the edge of the screen if you move your mouse cursor at one of the screen corners quickly enough, which means I'm constantly having to go and click the edge of the window to recall it.

It's irritating us both highly, and I couldn't find anything on it via google.
Anyone know how to turn this off?

tl;dr
how do I make windows stop flying off to the edge of the screen on a mac whenever I move the cursor quickly towards a corner

try looking for mouse gestures

I may be misremembering, but I do believe that I saw such an option, and I can assume that I would certainly have disabled something called mouse gestures or similar if possible, as I have a strong aversion to gesture recognition controls.
I guess I'll look for that again next time I'm there, though.

Its under "Expose and Spaces" in "System Preferences".