Epithelium is a type of tissue that forms the protective outer layer of the body and lines internal organs and cavities. It consists of closely packed cells with minimal space between them, which helps create barriers against pathogens and prevents water loss. Epithelium plays a crucial role in absorption, secretion, and sensation. There are several types of epithelial tissue, classified based on cell shape and arrangement. For example, simple squamous epithelium is a single layer of flat cells, while stratified squamous epithelium has multiple layers for added protection. Epithelial tissues are essential for maintaining the body's overall health and function.