Residue is what remains after something else has been removed, used up, or disappeared. When you wash dishes, the sticky film left in a glass after orange juice is residue. When a candle burns down, the hardened wax pooled at the bottom is residue. After rain evaporates from a window, you might notice water spots: that's mineral residue from the water.

The word often describes small amounts of substances that cling stubbornly to surfaces. Chemistry labs need to be cleaned carefully because dangerous chemical residues might remain in beakers and test tubes. Farmers worry about pesticide residues on crops. Even after you erase a pencil mark, you might see a faint gray residue on the paper.

Residue isn't always physical. People sometimes talk about emotional residue: the lingering feelings that remain after an argument or disappointment, like an uncomfortable heaviness that takes time to fade away.

The key to understanding residue is that it's the leftover part, usually unwanted or unintended, that persists after the main thing is gone. It's stubborn, it sticks around, and it often takes extra effort to remove completely.