According to its wiki, it's knees_together_feet_apart standing, in which case it doesn't need to be a tag IMO. In actual usage it appears to be used for both knees_together_feet_apart (whether standing or not) and legs_together, and a couple where it's hard to tell or neither quite fit (such as post #2745815, knees and toes together but heels apart).
What do we do with this tag? If we're going to keep it, the wiki needs changing and maybe some other tags should imply it.