This term most often refers to the browser cache. Cache significantly speeds up browsing by reducing the amount of data transferred and the overall load on the server.
Cache works by reusing data that was used in the past. Every web page is made up of many files, such as images and text, and downloading them can be very time-consuming.
The browser stores all this data as you go, and if you come back to the page, the stored data is used. For example, the same image is reused, because there is no need to download it again.
It can happen that the author of an article has replaced the images on the page, and the old image is loaded from the cache instead of the new one. In that case, simply refresh the page with the F5 key.
In the IT world, cache refers to any memory that makes working with and on a computer easier or faster. There is, for example, a hard disk cache or a content management system cache.