Null is the absence of a value. Null is typically used to indicate that a reference or pointer variable points to no object in memory.

From Wikipedia:

A null pointer has a value reserved for indicating that the pointer does not refer to a valid object. Null pointers are routinely used to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.