Ballet was a specific type of dance. Performances of this dance were called ballets. The female dancers were called ballerinas, the male dancers were called danseurs. It was important for ballerinas to have good arches in their feet.
As the child Annika Hansen, Seven of Nine dreamed of one day becoming a ballerina. In 2376, she dismissed this to Chakotay as having been a "juvenile fantasy," but Chakotay commented that "Those are the ones that stick with you." (VOY: "One Small Step")