The point or points at which two or more shapes cross or overlap one another.
The calculation of intersections can be used in game development to find things ranging from the when the paths of two objects will cross to the number of intersections between multiple lines. Intersections are a part of math.
This tag refers more towards the mathematics of intersecting shapes and structures in space. collision-detection should be used when referring specifically to the determining the collision between in-game entities outside the abstraction of their underlying geometries.