In this code, max_overflow is an argument for the QueuePool class from the sqlalchemy.pool module. It represents the maximum number of connections to create on top of the pool_size. This means that if all the connections in the pool are in use and a new connection is requested, a new connection will be created and added to the pool until the number of additional connections reaches max_overflow. In this case, the pool size is set to 5 and the maximum overflow is set to 10, so up to 15 connections can be created in total.