An association between a field in one table or query and a field of the same data type in another table or query. A join tells Microsoft Access how data is related.
When you add tables to a query, and those tables already have a defined relationship, Access automatically creates an inner join that selects records from both tables when the values in the joined fields are equal. Even if relationships weren't previously defined, Access automatically creates an inner join between fields that have the same names and data types if one of the fields is a primary key. You can also create joins manually. Access allows you to create inner joins, outer joins, and self-joins.