Rate
By definition, rate is a quantity which is typically measured by something that is being measured against something else or even a group of other things. It is used in different things including ratios and fractions, where the numerator and denominator are being measured against each other. These are used all the time in mathematics and science because in Physics people often measure things to one another, such as velocity of a fast particle to the speed of light. In math, we use them all the time whether it is a fraction, like 
, or a constant ratio of 50 pineapples per potato. These are also used in slope intercept equations as both slope, 
values and the 
intercept can be fractions which are ratios.
Example: 
where 
is being compared to 
