A riding habit was a woman's riding dress; consisting of a skirt worn with a jacket.
Yasmin Khan wore a riding habit of bottle green herringbone-tweed over a beige waistcoat and an ivory shirt during the year 1904, the 2021 Sontaran Invasion of Earth, and the Flux. (TV: Survivors of the Flux|The Vanquishers)
Missy, the feminine incarnation of the Master, wore riding habits with her ivory blouse; one in ebony black, (TV: Deep Breath) bottle green, (TV: Into the Dalek) burnt orange, (TV: The Caretaker) plum purple, (TV: Flatline) Prussian blue, (COMIC: The Master Plan) or violet purple. (TV: The Magician's Apprentice)