Headdress
When we talk about a headdress in anime art, we're usually not talking about generic hats or helmets. Instead, this tag mostly covers those elaborate, frilly hair ornaments that sit right on top of the head. You know the type—it's that iconic accessory that really ties a specific outfit together, often functioning more as a fashion statement than actual headgear.
Most of the time, you'll find these on maid characters. It's pretty much a requirement for the classic maid uniform, whether it's the crisp white brim seen on someone like Rem from Re:Zero or the softer, rufflier versions in Miss Kobayashi's Dragon Maid. But it's not strictly a maid thing. Gothic Lolita fashion is huge on this too. Characters in that style often sport headdresses loaded with lace, ribbons, and sometimes even artificial roses to match their dresses. It gives off a very specific, elegant vibe that fans of the aesthetic really dig.
Basically, if a character is wearing a detailed band of fabric that goes ear-to-ear over their head, it belongs here. It adds a lot of visual interest to a character's silhouette, which is probably why it's such a common trope in character design for games and light novels.