What is the name of the protein coat of a virus?

The protein coat of a virus is called a capsid. It surrounds and protects the virus’s genetic material, which may be DNA or RNA.

A capsid is built from repeating protein subunits called protomers. These units assemble into larger visible structural features known as capsomeres. Viral capsids commonly form helical or icosahedral structures, although bacteriophages and some other viruses have more elaborate shapes.

The capsid does more than act as packaging. It helps protect the viral genome from changes in temperature, acidity, and enzymes, and it can help the virus recognize and enter a host cell. During infection, the capsid or its contents must eventually release the genome in a process called uncoating.

Some viruses are enveloped. In those viruses, a lipid membrane surrounds the capsid, so the envelope is not the protein coat itself. The capsid together with the enclosed viral core is called a nucleocapsid, making “nucleocapsid” a related but broader term rather than the simplest answer to this question.