Definition: This two-word phrase indicates a ratio or fraction.

Example: There are 2 apples orange in the basket.

The two word phrase could be:  "For Every"

When we are writing a ratio or fraction, we are comparing two different quantities. 

Imagine that a track athlete has to run 3 miles for every day of practice. We could write the ratio 3:1.

Imagine that your parents are going to pay you $15 for every A on your report card. We could write the ratio 15:1

The key words are "For Every".