In second life the word collar can be used as a verb or a noun.
As a noun it means a scripted object which can pose or animate the wearer, either by the wearer's instruction or someone else's. Usually it signified some D/s relationship.
As a verb to collar means accepting a D/s relationship often Master/Mistress to slave. (See also Dom/Domme, Submissive, Pet) Collaring ceremonies are often held in second life, similar to marriages.