What is the significance of the error "Cannot redeclare class" in PHP?

The error "Cannot redeclare class" in PHP occurs when you try to define a class that has already been defined earlier in the code. This can happen if the same class is included or required multiple times in different files. To solve this issue, you can use the `class_exists` function to check if the class has already been defined before defining it again.

if (!class_exists('ClassName')) {
    class ClassName {
        // class definition
    }
}