A cache is temporary storage for data (determined by the website creator) from the visited web page.
Browser caching. The user’s device makes and stores a copy of various elements of the website. These can be scripts, text, or images. When you open a page, the browser cache helps to load all this much faster.
Caching on the server. All data is stored on the server. It stores the results of queries, which helps to avoid reprocessing the same information from the user.
In testing, in almost all cases, the rule is to clear the cache after each test pass (unless this is a purposeful test of the cache itself or the presence of a cache is required for some reason). The fact is that the cache obviously distorts the performance testing indicators, and can also cause a false bug report due to obsolete or inconsistent actual and stored data. In some cases, you cannot do without clearing the cache, even simply because of the huge amount of cached data.