Latency
In plain terms
The delay between making a request and getting a response.
Going deeper
Latency measures how long data takes to travel and be processed, often in milliseconds. Low latency feels instant; high latency makes apps sluggish. It's distinct from bandwidth (how much data flows).
Under the hood
Dominated by distance/round-trips, queuing, and processing; tail latency (p99) often matters more than averages for user experience.
Examples
Ping times, API response p99, database query time, CDN edge proximity.
Think of it like...
Like the gap between flipping a light switch and the bulb turning on: even if the wire is thick, distance and processing add a delay.