A caching plugin is a type of plugin for WordPress that speeds up the performance of a website by storing a cached version of pages and other elements of a website. This cached version is then served to visitors instead of the website having to generate the page each time it is requested.
When a page is first loaded, the caching plugin will store a copy of the page in the cache. The next time someone visits the same page, the caching plugin will serve the cached version instead of generating the page again. This reduces the amount of time it takes for the page to load and reduces the load on the server, making the website faster and more responsive.