Explanation/Reference:
In SQL Database, the relative measure of a database's ability to handle resource demands is expressed in Database Transaction Units (DTUs) for single databases and elastic DTUs (eDTUs) for databases in an elastic pool.
A pool is given a set number of eDTUs, for a set price. Within the pool, individual databases are given the flexibility to auto-scale within set parameters. Under heavy load, a database can consume more eDTUs to meet demand.
Additional eDTUs can be added to an existing pool with no database downtime.
References: https://docs.microsoft.com/en-us/azure/sql-database/sql-database-elastic-pool