Preloading

For example, in-game graphics are loaded before entering matchmaking rather than after it, reducing the wait time for other players once the match is set up.

This can be common assets such as props, all/some player characters, all/some non-player characters, and so forth. Or even everything you could possibly load. Or assets specific to earlier known criteria (e.g. matchmaking queue was entered for specific map/level so it preloads everything associated with that).

At face value preloading may sound like something all games do at level load, but this is pretty much the critical point where Something must be loaded which usually means all data related to the level. Preloading however means loading them before you have chance to play the level, so once the loading is done, it might take you the player far longer to reach the point where the level transition to the preloaded one actually occurs. Preloading in matchmaking implies loading the stuff before entering matchmaking queue rather than after matchmaking is done and people are ready to start, for other games it implies background loading or the whole game start being slower because it loads everything.