Fractions are a specific type of ratio that compares a part to a whole. Fractions are rational numbers written in the form $\frac{a}{b},$ where the numerator $a$ is the part and the denominator $b$ is the whole. There are many possible ways of reading fractions, but one universal method is saying $a$ over $b.$ Fractions where $a$ is less than $b$ are called proper fractions. Fractions where $a$ is greater than or equal to $b$ are called improper fractions. Fractions are also another way to write a division of the numerator by the denominator. A fraction like $\frac{18}{9}$ can be simplified to $\frac{2}{1},$ or just $2.$ It is important to keep in mind that the denominator of a fraction can never be equal to $0$ because the quotient of division by $0$ is always undefined.