What is latency?

The Internet is a system for transmitting things from one place to another, much like the postal system. Instead of letters and packages, the Internet transports information. Information can take many forms: an email, the picture and voice of the colleague you are talking to on video conference, or an important cat picture (see Figure 1). In the internet, information is put into packets and these packets are addressed and put “in the mail”. Then, a sequence of relays and transports convey those packets to the addressee. 

Latency is the amount of time it takes for a packet to get to its destination. It’s as simple as that.

Figure 1: Important cat picture

So, why does latency matter? It comes down to what you are trying to achieve when using the internet. For example, if you are having a video call, then it is very important that the latency is low and consistent. Otherwise, you may notice that the video and audio pauses or stutters, that people on the call keep interrupting each other, or that it’s difficult to play the “who speaks next” game.

For fast-paced interactive things like online gaming or AR/VR even very short periods of higher-than-normal latency can be annoying.

In addition to real-time interactions, latency can also affect things like web browsing. Imagine playing a game of chess with someone through the mail. You send your opponent a letter containing your next move and then wait for them to reply. How quickly that game will finish depends a lot on how promptly each of you answer, and also on how quickly the mail is delivered. In the same way, loading a website depends on many back-and-forth interactions between your device and the server hosting the webpage. If the network is slow (or even just sometimes slow), then loading the website can take a long time.