A non-slip surface is made so that your feet, shoes, or hands do not slide easily. Bathroom floors, bath mats, kitchen steps, shoe soles, and the inside of a tub often have a rough or rubbery finish for this. The point is safety: wet tile is easy to slide on; a non-slip layer gives you grip. Though actually, the label is a claim about the design, not a promise you cannot fall. Soap, water, and years of wear still win if the surface goes smooth. You will see the word on product packets more than in stories. Nearby labels are anti-slip and, especially in American English, non-skid (boats, cars, stairs).