For the part of a shirt, please see collar (clothing).
A pink collar
A collar was a round band of material worn around a pet's neck to identify or tether it.
In 2370, Spot wore a pink collar. She was later identified by virtue of the collar after reverting to an iguana due to Barclay's Protomorphosis Syndrome. (TNG: "Genesis")
In the late 32nd century, Grudge wore a collar with a tracker. If she became lost, Cleveland Booker, her owner, could locate her with a receiver he always carried on his body. In 3189, Michael Burnham reverse-engineered the collar, so she could locate Booker on Hunhau. (DIS: "Scavengers")