Proportion is defined as the comparative relation between things or parts. Proportion may also be used to reference the dimensions or size of an object or collection.
In math, a proportion is an equation that demonstrates two equivalent comparisons. An equation is written with two ratios in either fractional or colon form to demonstrate the relationship between them. In some cases, students must solve for a missing term to make the statement true. In other cases, students are asked to find a set of equivalent ratios to form a proportion. Cross products in a proportion are equal, which is helpful for allowing students to check their work after finding missing terms.