Fractions are a specific type of ratio comparing a part to a whole. They are 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 to read fractions; you can try some combinations below, but when in doubt, one universal method is to say $a$ over $b.$ Fractions are also another way to write division of the numerator by the denominator. $$\begin{array}{c}18÷9\iff \frac{18}{9}\end{array}$$ As such, a fraction like $\frac{18}{9}$ can be simplified to $\frac{2}{1}$ or just $2.$ Note: The denominator of a fraction can never be equal to $0$, since the quotient of division by $0$ is always undefined.