The basidium is a microscopic structure found in at the ends of hyphae in the fruiting bodies (usually mushroom-like) of basidiomycete fungi. The basidium usually bears four basidiospores.

The word basidium literally means little pedestal, from the way in which the basidium supports the spores. However, some biologists find that the structure more closely resembles a club; thus, the Basidiomycota are also known as the club fungi.