Definition of an "equivalent"
An equivalent is the factor of the number of molecules you need, at minimum, to carry out a reaction. The number of equivalent depends on your choice of what you consider is your main reactant.

Simply put, if you take a chemical equation where A + B → C, you need 1 eq. of B compared to A, i.e. you need one molecule of B for each molecule of A.

But sometimes, you can get something like 2A + B → C, and you want to know the "number of equivalent of B you should add to A". The quantity of B is one half that of A. If you consider your main reactant to be A, then you need to add only 1/2 (aka 0.5) equivalent of B.