what is a zooid?

A zooid or zoöid is a single animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals.
The zooids can either be directly connected by tissue or share a common exoskeleton.
The term zooid has historically also been used for an organic cell or organized body that has independent movement within a living organism.