Mule refers to a style of footwear which is backless or "no-back" and closed-toe. The more casual form of Mules are called Slides.
Mules were also defined as "half slipper" during the Colonial times.
Mules can be sporty, like mule sneakers, simple or elegant and has become a popular choice for women as well as men. Mules are made with different style/types of heels: high heels, low heels, wedge or chunky and if the backs are open and the toes are closed, they are considered Mules.
Mule is from the ancient Sumerian word "mulu". It was the original indoor "slipper", however, centuries later, Mules were fitted with a heel to become a fashion shoe.
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