A Cartesian product, or cross join, in SQL is a join operation that returns all possible combinations of rows from two or more tables. Imagine you have two tables: one listing customers and another listing products. A Cartesian product would generate a result set containing every possible pairing of a customer and a product, even if there's no logical connection between them. This can lead to extremely large result sets, often much larger than intended, and is usually not the desired outcome. While seemingly simple, it's important to understand when and why it might be needed. It's not a common operation in typical data analysis or reporting. Instead, it's more often used in specific scenarios, such as generating all possible combinations for testing or in very specific data transformation tasks. A proper join, like an inner join, would only return rows where a relationship exists between the tables, which is the typical and desired outcome in most cases. Incorrectly using a Cartesian product can lead to performance issues and incorrect results in larger databases.