What does overgeneralization mean

draw a conclusion or make a statement about (something) that is more general than is justified by the available evidence.

An overgeneralization would occur when a generalization was extended to situations that might not be true.

So an example: An accurate generalization might be that "Most women eventually want to be married." But the statement: "All women want to eventually marry" would be an overgeneralization, since there are probably some women who plan to be single all their life.