An overstaffed company, shop, hospital, or office has more workers than it needs. People are standing around; a smaller team could do the same work. Managers call a place overstaffed when they want to cut jobs or stop hiring. The opposite is understaffed — not enough people, everyone too busy. It is a workplace word, a little formal, more common in news and in offices than at the dinner table. You describe an organisation as overstaffed; you do not usually call one person overstaffed. Though actually, "too many staff" and "overstaffed" can hide a fight: the boss sees extra cost, the workers may see a team that finally has enough hands. It is not the same as overworked. Overworked means the people have too much work. Overstaffed means there are too many people.