What does epithelium refer to?

The term "epithelium" specifically refers to the cellular covering or lining of both organs and vessels. It is a fundamental tissue type that forms protective barriers and is involved in various functions such as absorption, secretion, and sensation. Epithelial tissue can be found on the outer surface of the skin (epidermis), lining internal organs, and covering various cavities.

In contrast, connective tissues serve to support and bind other tissues, muscle tissue is responsible for movement, and nerve tissue plays a critical role in transmitting signals throughout the body. Therefore, option B accurately encompasses the essential characteristics and functions of epithelial tissue.