The terms delay and latency are often used interchangeably by telecoms and IT people.
If we want to be “nit picky” there is a subtle difference but in the real world, they mean the same thing.
Essentially it means the time taken for some data to get from your computer to the destination, perhaps a website or an application. Often it is assumed to mean the time for that data to get to the far end and for a response to get back to your computer.
There are a couple of fundamental things that affect these delays.
The first is simple physics, and that is: the further the data has to travel the longer it will take. Data going from your computer to your printer will take a thousandth of a second (0.001 seconds), data going from New York to Washington might take 10 thousandths of a second (0.01 seconds) and data going from New York to Tokyo might take a hundred-thousandths of a second (0.1 seconds). These numbers assume the data is mainly going over cables (usually fibre optic these days) but if it goes via a satellite it has a lot longer to go (and extra 30,000km each way!) and thus the delays can increase tenfold or more.
The next thing that affects delays is the affect of the network equipment – a busy network router may have to leave your data in a queue for a while before it can forward it on to the next router.
Network link capacity can also affect delays because the links are busy and equipment has to queue traffic for a while before sending it on to the next router.
Finally, network loss, another subject in its own right, can affect delay because certain network protocols will resend any lost data which leads to huge increases in delay.
Often these delays are reported as “round trip delay” which are usually about double the one-way delay. In this case, the delays can be increased by the target website or application being very busy and taking its time to handle your data thereby introducing yet more delay.
In the real world, it is important to understand that delay, loss and throughput can all be interrelated………………..