What term describes a sheet of cells that cover internal or external surfaces of multicellular organisms?

The term that describes a sheet of cells covering internal or external surfaces of multicellular organisms is "epithelium." Epithelial tissue serves various essential functions, including protection, secretion, absorption, and sensation. It forms the outer layer of the skin and lines organs and cavities within the body. The structure of epithelial cells allows them to form tightly packed sheets, creating barriers between different environments, such as between the external environment and internal tissues.

Other choices refer to different types of tissues that have specific roles in the body's architecture. Stroma refers to the supportive tissue surrounding organs, connective tissue connects and supports other tissues, and endothelium is a specialized type of epithelium that lines blood vessels and the heart. While all these tissues play crucial roles in biological systems, they do not have the same broad coverage function that epithelial cells perform.