This sqadia.com short video clip is a brief explanation of Epithelium.
Epithelium is one of the four basic tissues of the body and is derived from all three germ layers. It is composed of very closely packed, contiguous cells, with very little or no extracellular material in the extracellular spaces. Epithelial membranes can be: Simple squamous epithelium, Simple cuboidal epithelium, Simple columnar epithelium, and Pseudostratified epithelium.
When there are two or more layers of cells epithelia is referred to as stratified, hence can be stratified squamous, stratified cuboidal and stratified columnar.