Difference between cache HIT and MISS?

This article will review some of the most frequent terms when it is about CDN and caching. It is really important to understand those terms in order to check the effectiveness of the content delivery and know how to check if the "Invalidation" process work.  

What is a cache-HIT?	What is a cache-MISS?
A "cache-HIT" happens when a file is requested from a cache and the cache is able to meet the request. For instance, if a user visits a webpage that's supposed to present a picture of a boat, the browser may send a request to the webpage's CDN for this image. If the CDN has a copy of the picture in its storage, then the request results in a cache hit, and the picture is sent to the user browser.	A "cache-MISS" is when the cache does not contain the demanded content. If a copy of the boat picture is not currently in the CDN cache, this request results in a cache miss, and the request is moved along to the origin server for the original picture. The CDN server will cache the photo once the origin server responds so that additional requests for it will result in a cache hit.

Finally, what is Cache-HIT Ratio?

Cache-HIT Ratio is a measurement of how many contents requests a cache is able to fill successfully, compared to how many requests it receives in total. A content delivery network provides a type of cache, and a high-performing CDN will have a high cache hit ratio in most cases, but this is not all you need to monitor and consider.