A ratio is a mathematical expression that compares two or more quantities, showing the relative size of one quantity to another. It is often written in the form of a fraction, such as 3/4, or with a colon, like 3:4. Ratios can be used in various fields, including finance, cooking, and science, to illustrate relationships between different values. Ratios can be simplified, just like fractions, to make them easier to understand. For example, the ratio 8:12 can be simplified to 2:3 by dividing both numbers by their greatest common divisor. This simplification helps in comparing ratios more easily and making calculations straightforward.