A physicsplosion is what sometimes occurs in video gaming when working with an unstable physics engine. It often happens when many physics-related things are taking place at the same time within a small area. The objects in motion, which are usually all touching each other, suddenly fly away from one another (or sometimes in random directions). This sudden and unwarranted blast of virtual pressure is what's known as a physicsplosion.
Alternative terms include physixplosion and physics explosion, the latter of which is where the term comes from. The term may also be applied to events in which objects in a game world are moving quickly and erratically without any real reason. Such things are probably the result of glitches in collision detection. This second kind of physicsplosion is usually referred to as a "spaz out."
Though there are many examples, one more well-known one may be the "get down" glitch from the N64 game Goldeneye (1997), which caused characters to spin and flail around a central point in their bodies when the game cartridge was not fully inserted into the console. This is an example of a "spaz out" physicsplosion.