Caching is where something is stored and re-used to prevent it from having to be created or downloaded again. Caching is a highly effective tool to increase the speed at which a webpage downloads.The two main kinds of caching are server side and client side.
Server side caching
Most modern websites use a language that runs on the server where the website is hosted. These server side languages allow developers to create more web pages in less time.
When someone requests a webpage, the server side language runs and assembles an HTML document to send to the client (the end user). The client’s device then renders the HTML document as a webpage.
Server side caching saves those HTML documents, so the server side language does not have to assemble it every time someone requests a webpage. Not processing the server side language to create an HTML document for each and every request saves a tremendous amount of server side processing power.
This also means that end users will not see updates to the website unless the server side cache has been cleared.
Client side caching
Browsers and devices also save items and re-use them in order to speed things up.
If you have visited a web page (and client side caching is properly configured), the browser will store a copy of major website elements. This means that even if the server side cache has been cleared, you may not see up to date changes.
Your browser will most often render the copy of a webpage you have stored locally, and not re-download the newest version. To see the most up to date changes, you need to clear your client side cache. For Chrome, this extension is a DREAM for developers. I use it and have it set to clear my entire cache and auto reload the page.
Many people think a “hard refresh” will clear your cache, but most often it does not. Also keep in mind that each browser has it’s own unique cache, which needs to be cleared.