What is the difference between pass by value and pass by reference in programming?

Pass by value and pass by reference are two ways that programming languages can handle passing parameters to functions.

**Pass by value:**
In pass by value, a copy of the actual value of the argument is passed to the function. This means that any changes made to the parameter inside the function will not affect the original value of the argument outside the function. Pass by value is usually used for primitive data types like integers, floats, and characters.

**Pass by reference:**
In pass by reference, a reference to the original value of the argument is passed to the function. Any changes made to the parameter inside the function will directly affect the original value of the argument outside the function. Pass by reference is usually used for complex data types like arrays, objects, and structures.

In conclusion, the main difference between pass by value and pass by reference is whether a copy or a reference to the actual value of the argument is passed to the function, leading to different behaviors when modifying the parameter inside the function.