The side of sheath attached to head region in bacteriophage is termed as

Explanation

The collar of a bacteriophage is a structural component that connects the capsid to the tail. It serves as a junction between the head (capsid) containing the viral genetic material and the tail, which is used for attachment to host bacteria and injecting the viral genome into them. The collar is typically made up of protein subunits and may play a role in the phage's ability to recognize and attach to specific bacterial surfaces.