A collar is something which goes around the neck of a person, animal, or thing (such as a bottle).
Specifically, collar may mean:
Collar (clothing), the part of a garment that fastens around or frames the neck.
Collar (animal), a strap for an animal's neck to which a leash or harness may be attached.
Collar (BDSM), a device of any material placed around the neck of the submissive partner in BDSM.
Collar (jewelry), an ornament for the neck, especially a close-fitting necklace popular in the Edwardian period and sporadically thereafter, or a livery collar worn around the neck and shoulders as a mark of office.
Collar (finance), a combination of an equal number of call and put options at slightly different exercise prices.
Collars is also used metonymically (and usually in a derogatory manner) to refer to members of the clergy, most often by disgruntled church musicians.