In JavaScript, 'null' is a value that represents the intentional absence of any object value, while 'undefined' is a value that indicates the absence of a defined value.
'null' is used to indicate that a variable or object is intentionally empty or has no value.
It is a primitive value that is often used to initialize variables that are meant to later hold an object value.
'undefined', on the other hand, is a value that is automatically assigned to variables that have been declared but have not yet been assigned a value.
It is also returned by functions that do not explicitly return a value.
In JavaScript, 'null' is considered an object, while 'undefined' is considered a type.
Overall, 'null' is used to represent the absence of an object value, while 'undefined' is used to represent the absence of a defined value.