(1) Epithelial relates to the layer of cells which form a covering over the internal and external surfaces of the body. Examples of this would be the inner lining of the lungs, digestive tract, and skin cells.
This type of epithelial tissue does what it sounds like it does: lines things. What structures it lines depends on whether the lining is simple or stratified.
Stratified epithelium is several layers thick and lines the skin, mouth, and anal canal. Squamous cell carcinoma is an example of a cancer that develops from lining epithelium.
Glandular epithelium forms glands. Glands secrete things and are classified as endocrine or exocrine. Endocrine glands secrete things into the bloodstream, like hormones. Exocrine glands secrete things that go outside of the body, like mucus and sweat. Cancer of a gland is called adenocarcinoma.