It indicates whether a network connection is not metered. Meaning that the data usage on this network is not restricted by cost/pricing concerns.

Usage Scenario:

It means the network is considered unlimited or free, e.g. an unmetered Wi-Fi connection. If it is false, it means the network is metered e.g. a mobile data connection with a data cap.

Most home and office Wi-Fi networks are unmetered by default.

A user can manually mark a Wi-Fi network as metered in the Android settings. This would make this return false.

Some carriers offer -unlimited data plans where certain networks may be marked as unmetered.

Some SIM-based internet providers may mark their connection as unmetered.