The delay between sending a request and receiving a response. Like the time it takes between asking a question and getting an answer.
Online gaming requires low latency - players notice if there's more than 50 milliseconds delay between their actions and the game response.
Latency is a performance metric (time delay), not a standalone cloud service. All cloud providers measure and influence latency through networking, regions/edge locations, load balancing, CDN, and routing services.