WITH starts a common table expression (CTE)

A CTE gives a query result a temporary name so you can reference it in the main query. Here, recent_orders is the CTE's name. The CTE is available only to the SQL statement immediately following it — it is not saved and it is not a temporary table. Once that statement finishes, the name is gone.

WITH recent_orders AS (
  SELECT *
  FROM orders
)
SELECT *
FROM recent_orders;