Stratified epithelial tissues are a type of epithelial tissue where the tissue possesses multiple layers of cells. The adjectival name is derived from the geological concept of strata (sg. stratum).
Stratified epithelial tissues possess multiple cell shapes; columnar cells are prevalent at the innermost layers, closest to the basement membrane, and compress over time, leading to the prevalence of squamous and cuboidal cells towards the free surface layer. As a result of this variation, when stratified epithelial tissues are named in full, the cell shape term is taken from the cell shape which is present on the free surface layer.
Due to the dense packing of the tissue, stratified epithelial tissues are most commonly found in areas that endure significant amounts of frictional stress or areas that require dense covering. Examples include animal skin and the lining of the mouth and throat.
Pseudostratified epithelial tissues are not true stratified epithelial tissues (hence the pseudo- prefix). They are a type of simple epithelial tissue with one layer of epithelial cells.