A backless shoe that leaves the heel exposed.
A mule leaves the heel exposed because the shoe has no back section enclosing it. The front upper holds the foot while the heel remains free, so the defining feature is the open back rather than the height of the heel. Christian Louboutin’s Dolly Mule has a 100 mm stiletto heel, while the V&A records a block-heeled mule designed by Roger Vivier for Christian Dior around 1960. These examples show why a heel description alone cannot identify a mule. The term describes a structural feature shared by shoes with different heel shapes and heights.
In job listings
This word belongs to design briefs and the sales floor. Because a mule has no back, a footwear advisor may talk a client through fit and how it stays on, and a designer has to account for the same question in the shape of the vamp. Search local jobs for “footwear”.