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In computing, "null" represents the absence of a value or a pointer to nothing, indicating that a variable does not have a valid data or an object assigned to it. It is used to signify an empty or unknown state, and its specific meaning can vary depending on the context, such as being an empty value in programming, a marker for a missing data field in a database, or the zero-valued ASCII character that marks the end of a string.

In programming it represents absence: Null is a special value that means a variable does not point to any object or contain any data.

Placeholder: It is used to explicitly show that a variable is intentionally unassigned.

Prevents errors: Assigning null can prevent errors by handling cases where a value is expected but not present.

Null pointer: A null pointer is a pointer that does not point to a valid memory address, signifying the absence of a usable location.

In databases

Missing data: NULL is a special marker in SQL that indicates a data value does not exist, is not known, or is missing in a particular field of a record.

Result of joins: NULLs can appear in the results of certain database queries, such as outer joins, to show rows that don't have a match in a related table.