The stem of the mushroom is known as the stipe.
Many people don’t realize that the tip of a mushroom is actually called the stipe. The stipe is an extension of the cap and contains some gills, although not all mushrooms have gills. It also has a partial veil, which is a layer that covers up the gills until they are ready to be used. The veil breaks apart as it matures and allows for spores to be released.