Stereocilia (or stereovilli) are apical modifications of the cell, which are distinct from cilia and microvilli, but closely related to the latter.
Though their name is similar to cilia, they are actually more closely related to microvilli, and some sources consider them to be a variant of the latter, rather than their own distinct type of structure. In structure, they are longer than typical microvilli, and have more of the characteristics of the cellular membrane proper.
They are characterized by their length (distinguishing them from microvilli) and their lack of motility (distinguishing them from cilia). They contain actin filaments.