Skin that's callused has become thickened and tough with use. Your callused hands are evidence of the hard work you do at your summer landscaping job.
If you spend hours rowing a boat, lifting weights, using a shovel, or even writing in a notebook with a pen, your fingers are likely to become callused. This natural condition is your body's way of protecting itself from friction or pressure. A blister at the back of your foot will gradually become a callused heel if you keep breaking in those new shoes. Callused derives from the Latin callum, "hard skin."