At OOFOS, W will always denote "women's" and M will always denote "men's", to help determine which size is right for you. We do not offer wide width shoes at this time, so all our shoes will be a medium width with the exception of our OOlala sandal which is narrow. Unisex products will have the men's and women's sizing equivalents listed together, for example M5W7 or M10W12. The M and W denote which size it is for the respective gender, and not a medium or wide width.