Bug

Definition · applies to programs

Elementary

A bug is a mistake in a program that makes it behave incorrectly.

Examples

Things that may be mistaken for examples.

In floating point arithmetic, $0.1 + 0.2$ evaluates to $0.30000000000000004$ due to rounding errors. High school
The rounding in $0.1 + 0.2$ is not a bug unless the code assumes that the result is exactly $0.3$.
In Python, opening a file that does not exist raises FileNotFoundError High school
The FileNotFoundError is not a bug, because a missing file is an expected condition, not a mistake in the code.