The Connection interface provides a handle to the device’s connection information.
A connection is metered when the user’s connection is subject to a limitation from his Internet Service Provider strong enough to request web applications to be careful with the bandwidth usage.
What is a metered connection is voluntarily left to the user agent to judge. It would not be possible to give an exhaustive list of limitations considered strong enough to flag the connection as metered and even if doable, some limitations can be considered strong or weak depending on the context.
Examples of metered connections are mobile connections with a small bandwidth quota or connections with a pay-per use plan.