Latency
Also called: Ping, Round-trip time
The delay before data starts arriving, measured as a round trip in milliseconds.
Definition
High latency makes every request slow to start, even on a fast connection. It's why apps feel sluggish on satellite or congested mobile networks.
In practice
A 600 ms round trip means an app that makes 5 requests in a row waits 3 seconds before showing anything.