The fractional part of a nonnegative real number is the part of the number that appears after the decimal point. For example, the fractional part of $\frac{7}{3}$ is $\frac{1}{3}$

To be more precise, for $x \in \mathbb{R}$ with $x \ge 0$ the fractional part of $x$ denoted as $\{x\}$ is given by $\{x\}=x-[x]$ where $[x]$ denotes the integer part of $x$

The name ``fractional part'' is somewhat of a misnomer: To the novice, the name may seem to imply that the result must be a fraction (and therefore rational), which is not the case. For example, $\{\pi\}=\pi-3$ which is not rational.