what is
What is GID in Mac OS: BSD , each user can belong to one or more groups. Each file-system object.

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GID definition

Explanation: Group ID. A unique identifier for a collection of users. In BSD , each user can belong to one or more groups. Each file-system object has an associated GID that is used to determine the object’s permissions . Each process has an associated group list . See also process GID

More definitions for Mac OS users such as GID in Dictionary G.