She's not a big character in Harry Potter, but her name made an impression.
Madame Rosmerta (pronounced "rohz-MER-tah") first appears in Harry Potter and the Prisoner of Azkaban. She is the owner of the Three Broomsticks, a pub in Hogsmeade that the three heroes and the teaching staff at Hogwarts like to visit. She is described as an attractive woman with a curvy silhouette. But she is quite old, as she was working as a barmaid when James Potter and Sirius Black were students.
This name is likely to appeal to people who like "rose" names, like Rosetta, Rosalind, or Rosario. But Rosmerta has nothing to do with the flower. Rosmerta is a Gaulish (an extinct pre-Celtic language) name meaning "the great provider," and is in reference to a goddess.
There's a lot of talk about pantheons in Neo-Paganism. Pantheons are a relatively new concept made to catalog gods into their designated cultures/countries and keeping them there. In reality, it's not quite so cut and dry. Deities like Rosmerta (and also Epona) are a testament to that. Rosmerta is a goddess for both the pre-Celts and the Romans.
After the Romans conquered the area where the Gauls resided, they adopted Rosmerta as their own. She became a consort of Mercury, the messenger god of trade. Rosmerta is a goddess of fertility and abundance. She is sometimes shown holding a caduceus wand, which would suggest that she is responsible for healing magick. As for her original position as a pre-Celtic goddess, not much is known about what exactly she presided over. In their artwork, she is depicted holding a cornucopia. Some sources state that she is the goddess of sacred springs (which would make it appropriate for the owner of a pub) and other sources list her as a goddess of fire.
I like this name a lot. Due to her association with the cornucopia, Rosmerta would be an excellent choice for someone born during the harvest or on a harvest holiday like Lammas, Mabon, or the American Thanksgiving. The goddess has no negative stories associated with it (that we know of anyway) so even the camp that is wary of using the names of deities will have little to fear. It's kind of a wonder that this name isn't used more often.