A metered connection is an Internet connection that has a data limit associated with it. Cellular data connections are set as metered by default. Wi-Fi and Ethernet network connections can be set to metered but aren't by default. Some apps might work differently on a metered connection to help reduce your data usage. Also, some updates for Windows won't be installed automatically.
To set a Wi-Fi network connection as metered:
Select Start > Settings > Network & Internet > Wi-Fi > Manage known networks.
Select the Wi-Fi network > Properties > turn on Set as metered connection.