Calluses are areas on your feet -- usually found around the heel, ball of the foot and on the side of the big toe -- where the skin has hardened due to constant pressure and friction. An athlete, like a runner or dancer, will have calluses thanks to consistent practice. Likewise, footwear like high heels or tight shoes can have the same effect.
To treat calluses, you have a few options. There are pumice or callus stones that you use, preferably on damp skin, to soften the callus and any snags or rough patches. Another tool that some women prefer is a foot file -- similar to a callus stone, it has a bit more abrasion to it to smooth the skin. (You can also use these tools just to take dead skin off your heels.) Regardless of what you use, stop if it hurts or if you break the skin.
The key here is to smooth the callused area, not remove or cut the callus. Aside from the infection risk, calluses, however unattractive, protect our feet. Taking away that protective layer is like putting baby skin in the sun without SPF; the skin is vulnerable. I learned this lesson the hard way when I had a pedicure (and got my calluses shaved) the day before a tennis match. I don't remember if I won or lost but I do remember hobbling to the bathroom that evening to soak my newly blistered feet.