Satellite collision

Strictly speaking, a satellite collision is when two satellites collide while in orbit around a third, much larger body, such as a planet or moon.
This definition can be loosely extended to include collisions between sub-orbital or escape-velocity objects with an object in orbit. Prime examples are the anti-satellite tests by the US and China (see below).
Natural-satellite collisions.
There have been no observed collisions between natural satellites of any Solar System planet or moon. Collision candidates for past events are:
Artificial-satellite collisions.
Three types of collisions have occurred involving artificial satellites orbiting the Earth:
Satellite collision avoidance.
Satellite operators frequently maneuver their satellites to avoid potential collisions. One notable near collision was Sept 2019 between an ESA satellite and a SpaceX Starlink satellite, when ESA tweeted/complained at having to move to avoid the Starlink satellite.