It is commonly used among bandwidth providers, e.g. datacenters and upstream providers, for both capacity planning and/or calculating metered use and roughly means "for most of the time this was the throughput on the line".
It is commonly used among all major internet transit and peering networks, as well as datacenters and ISPs for both capacity planning and/or calculating usage. It roughly means "for most of the time this was the throughput on the line".