Latency
The time delay between sending a request and receiving a response, measured in milliseconds.
Latency is how long data takes to travel from point A to point B. Low latency (under 20ms) is critical for gaming, video calls, and financial trading. High latency (100ms+) causes noticeable lag. Latency is primarily determined by physical distance (light travels through fiber at ~200,000 km/s, so NY to London takes ~35ms one-way) and the number of network hops. Satellite internet has inherently high latency (500-600ms) because signals must travel to space and back.