1. A dot is a single pixel on a matrix display.
2. Single small dot on a dot matrix printer print out.
4. In a RPG or MMORPG, a DoT is short for Damage Over Time and is a spell or other damage that causes a player or creature in a game harm for a short period of a time. For example, a player hit by a poison spell could be poisoned for several seconds unless they are cured.