The relationship between capacity
fluid ounces

Answer
Fluid ounce is a fraction of a capacity.

Explanation
Capacity is a term is define how much a container can hold a liquid. It is defined as the maximum amount of something that a container/object can contain.
Fluid ounce is a unit of capacity which is equal to one twentieth of a pint. Where a pint is a fraction of a litre which is approximately (28/100)of a litre.