I've heard this term used many-a-time in StarCraft 2 (and 1) replays on the web. At first, I always assumed it meant the player was sending out an attack force at a specific time in the game that's considered a good time to push out, or inside what is considered to be an optimal window of attack.
But the more videos I watched the term seems to be used when the player is just attacking, regardless of when/why/how, and about the scenario in which it isn't used is when a player counter-attacks after successfully defending another players timing push (and then they just call it counter-attack).
So why do they call it timing push? And not just "attacking". Or is it in fact only (properly) used at certain "times" during the game?