Anumber that is compared to 100 is a ratio called a proportion percent

The comparison of two numbers is called a proportion, sometimes a fraction.
For example, 
2:5  is a proportion, meaning compare 2 with 5
2/5  is a fraction (that means divide two by five)

Since we use fractions a lot, and to make it convenient, we would multiply the fraction by a 100, and call the resulting number percent, abbreviated (%).  ("cent" means 100 in Latin, which is the root of most European languages).  So instead of the clumsy way of writing (or saying) 2/5, we would say (2/5)*100%=40%  (forty percent).

In summary, whenever we compare a number to 100, is a ratio called percent.