Viral envelope

Outermost layer of many types of the infectious agent

A viral envelope is the outermost layer of many types of viruses. It protects the genetic material in their life cycle when traveling between host cells. Not all viruses have envelopes. A viral envelope protein or E protein is a protein in the envelope, which may be acquired by the capsid from an infected host cell.

This keyword could refer to multiple things. Here are some suggestions: