In plain English
Latency is the wait. Every time you tap a button, data has to travel to a server and back. The farther it goes and the more stops it makes along the way, the longer you wait.
Example
A player in Madrid connected to a game server in California sees about 150 milliseconds of latency, so every move feels slightly late. Switching to a server in Europe cuts it to about 20.
In short
The wait, not the speed. How long one request takes to get an answer.
Why it matters
Latency is a big part of whether an app feels fast. Video calls, games, payments and AI chat all suffer when it's high. With AI tools, teams track how quickly the first words appear. CDNs, caches and servers placed closer to users are common ways to cut it.
Common confusion
Latency vs. bandwidth. More bandwidth doesn't fix high latency. A wider pipe moves more data at once, but each trip still takes just as long.