The word rinse means to wash off or to run water over. Rinse water is describing water you are using for cleaning or sanitation. It's just normal water, but by using "rinse" you can be more descriptive. Just like if you were to say "drinking water." A common example might be if I were to get some dirt on my hands, I'd go rinse my hands off with soap and water. Or use that rinse water to wash off those apples before you eat them. It's not all that commonly used.

I would add that rinse water is generally clean water. After washing dishes in soapy water, for example, they would be next put in clean water to rinse away the soap.

I hate to disagree, but "rinse water" is the combination of clean water and the residue, detergent, dyes or other things that are left behind when something is washed and/or soaked in water. In the case you quoted above, the dish is first cleaned with a cloth and soap, then dipped or dunked into another container (sink, basin) filled with water. The difference is that it eventually becomes slightly soiled, dirty or soapy. The benefit is only a small amount of water is necessary because it is reused for each soapy dish.