The viral envelope is only present in some viruses, primarily those that infect animal cells.
The viral envelope surrounds the protein coat and is made of a portion of the host's cell membrane. Viral envelopes help the virus to enter the host cell.
The viral envelope is also known as the lipid envelope, because it contains lipids.
Glycoproteins (proteins that contain sugar chains) are present on the outside of the envelope. These proteins bind to receptor sites on the host's cell membrane and allow the virus to enter the cell.