Controller class names are pluralized. The reason is the controller controls multiple instances of object instance.

For Example: OrdersController would be the controller for an orders table. Rails will then look for the class definition in a file called orders_controller.rb in the /app/controllers directory.

For Example: PostsController would be the controller for a posts table.

If the controller class name has multiple capitalized words, the table name is assumed to have underscores between these words.

For Example: If a controller is named PendingOrdersController then assumed file name for this controller will be pending_orders_controller.rb.