Alternate costumes of official origin, whether it be from the creators themselves, or from second-parties involved in the given copyright. Generally a costume other than the standard one the character appears in.
These can often times appear in manga/anime (beach episodes, as one example), video games (whether as unlockables or as skins to be bought in gacha games), and on special events. Figures which can have such costumes include Virtual YouTubers.
Only use this tag for official costumes of the wearer themselves. If the character is wearing an official costume belonging to another character, use alternate costume or cosplay instead as applicable.
Do not use this tag with alternate costume, the tags are mutually exclusive.