A ballerina
Ballet is a specific type of dance. Performances of this dance are called ballets. The female dancers are called ballerinas, the male dancers are called danseur. It is important for ballerinas to have good arches in their feet.
Julian Bashir was once in love with a ballerina named Palis Delon. The relationship ended when Bashir graduated from Starfleet Academy and accepted a posting on Deep Space 9. (DS9: "Armageddon Game")
Kathryn Janeway danced The Dying Swan during a talent night aboard the USS Voyager in 2373. She had learned the dance while taking ballet classes when she was six years old. (VOY: "Coda")
A crew member of the USS Enterprise-D hallucinated that she was a ballet dancer while the Enterprise was at the edge of the known universe. (TNG: "Where No One Has Gone Before")