Ballerina skirt is a full skirt that reaches to mid-calf or just above the ankles, often made up of multiple layers of fabric. It was a popular style during the 1950s. It is based on the romantic tutu length.
Ballerina skirts have been a consistently popular length for formal dresses, especially for young women.
In geophysics, the term is used to refer to a wavy almost-circular region produced by perturbing the equatorial current sheet in a magnetic field whose shape resembles a tutu sticking out from a ballerina's waist.