Unit rate is the ratio of cost: number of units. Then the ratio is simplified so that the number of units is 1.
Having a knack for unit rates can make you a smarter shopper. For example, let's say that you are craving some cheesy, crunchy goodness and are trying to decide between two bags of chips. The Shmoritos are $4.50 for 12 oz. Shmingles are $2.50 for 7.75 oz. You obviously want the most munch for your money, so which bag to buy?
To solve this crunchy conundrum, compare the price per ounce for each bag.