A join in the context of databases, particularly in SQL, is a method to combine rows from two or more tables based on a related column between them. It allows retrieving information from multiple tables in a single query by specifying the conditions for the rows to be matched. Common types of joins include INNER JOIN (returns matching rows), LEFT JOIN (returns all rows from the left table and matching rows from the right), and RIGHT JOIN (returns all rows from the right table and matching rows from the left).