Have you ever wondered what Hot Corners were?
If you’re a baseball fan, you know that third base is known as the hot corner–because of how a sizzling ground ball can make a subpar third baseman look like he’s playing dodgeball rather than baseball.
Not to be outdone, the Mac has four hot corners, one in–surprise!–each corner of the screen. You can use these hot corners to accomplish tasks with the flick of a finger that might otherwise require a more precise clicking of a dock icon or burrowing through a couple of levels of system preferences.
Source: How to use Hot Corners on Mac