Web browsers and some intermediate Internet routing servers retain copies of frequently used web content for a short period of time to avoid the the need to fetch them from the original source every time. These are called cached files and they are stored on a computer or in a computer folder called a cache. Cache is pronounced either like “cash” or with a long “a” more like caish, let’s not get into a debate about which is right (but it’s cash, OK?) but be open minded and accept either variant, there are those who pronounce it cashay but let’s ignore them, they’re probably foreigners.

Caching saves the cost sending data tens of thousands of miles through sometimes expensive routes (like satellite links) and delivers web pages faster.
The down side is that some bits of content may not be bang up to date.
Caches are usually very short-lived so the negative impact is seldom noticed. On the other hand people often revisit pages of a website several times in the space of a few minutes so after the first visit they are delivered instantly from the cache in the users web browser.

The good news is that normal users are rarely inconvenienced by caching and then seldom need any more the CTRL-F5 to force a page-refresh (that’s to say: press Function key 5 while holding down the CTRL key).

When Caching does cause a problem the fix is to flush (empty) the cache using CTRL-F5 on a Windows PC. Usually it’s only website developers that have the problem because we need to see that a change we’ve made has worked as intended.  Files may be cached in multiple locations on the route from the original server to a particular end-user. The end user may have data cached by both his web browser and his PC.  That means if he uses multiple different browsers (again it’s only really computer geeks that find it necessary) a file cached by, say Google Chrome might also be cached by MS Windows so if he accesses the same page using MS Edge or Firefox the file may still available from a cache.
Similarly your Broadband provider may use caching.  That means if many of their customers are reading the front page of The Times, the provider needs to make less use of his expensive high capacity internet connection, he just lets all his users read the same copy. Flushing some of those other caches can be more difficult to implement.  A web developer will be able to flush the cache on the web server and some access levels to WordPress include a “flush cache” control.
A (slightly less) complicated way to clear many of the intermediate caches is to use a VPN to briefly route your internet connection via a different country but I’ll not go into detail here.
I know it’s beginning to sound complicated, you should have stopped reading sooner!
You may wonder about web sites subject to extremely frequent update, share prices might be an example. In such situations the server can effectively tag files with a label that means “don’t cache me”. That’s very effective but there’s noting to stop some caches being configured to disregard that tag.