The Cute Mark Crusaders is the name used by three young fillies to describe their organization. Often abbreviated to the CMC, the Crusaders consist of Apple Bloom, Scootaloo and Sweetie Belle. The purpose of their organization is to discover their cutie marks, as well as mutual support and friendship.
In episode 4 of season 3: "One Bad Apple," Apple Bloom's cousin Babs Seed comes to visit from Manehattan. Although she initially bullies the Crusaders and becomes friends with Diamond Tiara and Silver Spoon, she is eventually revealed to have been the victim of bullying herself. The CMC forgive her and offer her their friendship once more, which she accepts. She then joins them as the fourth Crusader.
This tag should only be used for at least three Crusaders together; it should not be used for any post that shows only one or two of the Crusaders unless they are specifically and obviously involved in activities related to the group. It may be used for posts that show items directly pertaining to the Crusaders (their cloaks, patches, etc).