Website caching means keeping ready-made copies of a website's pages, so that the server does not have to build each page again for every reader. A cache is a store of such copies. Caching makes a site load faster, and it lets the same servers handle far more readers. For a news site, this matters because readers leave a page that loads slowly.
Why does a page need building at all? A news page is not stored as one finished file. When a reader asks for it, the server collects the story from a database, adds the headline, the photos, the list of related stories and the ad spaces, and assembles them into a page. This can take most of a second. That is fine for a few readers. It is too slow when thousands of readers ask for the same page in the same minute.
Here is how it works on a busy day. Say the Maharashtra state board publishes its Class 10 results, and a Marathi news site in Pune publishes a story with the link. In the first minute, 20,000 students and parents open the story. The first request reaches the server, which takes 0.8 seconds to build the page. The caching tool then saves a copy of the finished page. The next 19,999 readers receive that copy, each in about 0.05 seconds. The database is asked once, not 20,000 times.
Then the editor corrects a mistake in the headline. The old copy is now wrong. So the newsroom CMS tells the cache to delete it. This is called clearing, or purging, the cache. The next reader's request builds a fresh page, and the cache saves that one.
Caching happens in several places. The page cache on the publisher's own server is the one described here. A content delivery network (CDN) keeps copies on servers in many cities, so that a reader in Nagpur receives the page from a nearby server. The reader's own browser also keeps copies of the logo and the fonts, so that it does not download them again. And inside the server, an in-memory cache keeps the most-used data, such as the list of top stories, in memory instead of on disk.
What is not cached? Parts that differ for each reader, such as the ads and the paywall message, are added separately, after the copy is served. If they were saved in the copy, every reader would see the first reader's ads.
Search engines also measure how fast a page loads, and they may rank slower pages lower. So caching affects how many readers arrive through search, not only how long they stay.