You click a link and wait. The page takes a second to load. That delay is latency — the time between an instruction and the response. It is measured in milliseconds. Low latency feels instant. High latency feels sluggish. For gaming, video calls, and financial trading, latency matters more than bandwidth.

Latency comes from many sources. Distance is one. Data travels at the speed of light in fiber, but the world is large. A round trip from New York to London takes about 60 milliseconds minimum. Processing time in routers and servers adds more. Congestion makes it worse.

Sources of latency

• Propagation delay: time for signal to travel
• Transmission delay: time to push data onto the link
• Processing delay: time for routers to forward packets
• Queuing delay: time waiting in buffers

Content delivery networks reduce latency by caching data closer to users. Edge computing pushes processing to the network edge. For autonomous vehicles and remote surgery, every millisecond counts. Latency is not just an inconvenience. It can be a safety issue.