Collaring is a formal step in a BDSM dynamic that makes said dynamic "official". Typically marked by a ceremony, sometimes with other members of the kink community in attendance, other times in private. The collar is typically given by a Dominant person to a submissive person and is often placed on them by Dominant.

Collaring is an extremely intimate choice to make - sometimes even changing some parameters of the dynamic from how they were "pre-collaring". For some people collaring is similar to a marriage vow.