A Proportion

1. (countable) A quantity of something that is part of the whole amount or number.
2. (uncountable) Harmonious relation of parts to each other or to the whole.
3. (countable) Proper or equal share.
4. The relation of one part to another or to the whole with respect to magnitude, quantity, or degree.
5. (mathematics, countable) A statement of equality between two ratios.
6. (mathematics, archaic) The "rule of three", in which three terms are given to find a fourth.
7. (countable, chiefly in the plural) Size.