When you think of the word encroachment, you think of somebody stepping over a line from their side to yours. For the football fans out there, we hear the word all the time when the defensive team goes over the neutral line prior to the ball being snapped.
In real estate it is not all that different. An encroachment is the physical intrusion of a structure or improvement onto the land of another. Other examples could be a fence or a driveway over the property line.
Remember that your property line extends upward to the sky, so a tree hanging onto your property is encroachment as well.
An encroachment can be found by a survey. Encroachment is a form of trespass, so when an encroachment occurs you may be able to sue your neighbor for trespass.