In PostgreSQL and SQL in general, the `WHERE` clause, combined with the `IN` operator, is used to filter rows from a table based on a specified list of values. It allows you to retrieve rows that match any of the values provided in the list. The `IN` operator simplifies querying for multiple values without the need for multiple `OR` conditions.

Example:

SELECT column1, column2, ... 
FROM table_name 
WHERE column_name IN (value1, value2, ...);