Final answer:
Operator overloading is when a programmer supplies behavior that occurs when built-in operators are applied to user-defined types.
Step-by-step explanation:
When a programmer supplies behavior that occurs when built-in operators are applied to user-defined types, it is called operator overloading. Operator overloading allows the programmer to define the behavior of operators such as +, -, *, / when used with custom-defined types. This provides flexibility and allows for more intuitive and convenient coding.