The `!=` (not equal to) or `<>` (not equal to) operator is a fundamental comparison operator in SQL. It's used to identify rows where a specific column's value does not match a given value. This is essential for filtering data based on conditions. For instance, you might want to select all customers who haven't placed an order in the last month. Or, you might want to find all products whose price is not equal to $10. The `!=` and `<>` operators are interchangeable in most SQL dialects, although `!=` is more common in some systems. Using these operators allows for precise data selection and manipulation. They are crucial for building complex queries that require specific criteria for data retrieval.