Cache is very common and can sometimes be confusing when trying to understand the different methods behind the it works and how you can utilize it in the many different ways which help the web be a better and more enjoyable place for users. Wiki defines cache as a component that stores data so future requests for that data can be served much more quickly.
Servers use caching to help reduce CPU loads and usage. Web browsers use a cache to render website pages faster for users, so they do not have to wait as long for the website page to load. Routers cache DNS Internet Protocols to send and receive those requests faster so the web browsers can operate at a higher performance level. CDNs are built and designed utilizing cache in ways you would think are unheard of. Although most CDNs do not cache HTML files which should not be needed in the first place, they do however cache many elements HTML uses.
When it comes to websites, caching is always going to be one of the most critical for making web pages load faster. All the other caching elements take that speed and boost it. As you may or may not know, it is a good idea to clear your web browser cache every now and then. Web browsers are getting better at removing a regulated amount more frequently by eliminating cache after a certain amount of time passes, but always keeping just enough to make your web surfing enjoyable by remembering pages you visit. A cache copy is kept in reserve, so it will appear faster if you visit that same page again and without you having to wait so long, for it to load. Microsoft antivirus software does this usually by default.