Apache (officially called the Apache HTTP Server) is a free, open-source web server software that takes requests from web browsers (like Google Chrome or Safari) and serves them the files, images, or code needed to display a website.
Think of Apache as the waiter in a restaurant: a user sits at a table (the browser) and asks for a specific dish (a website URL like ://example.com). Apache takes that order, fetches the food from the kitchen (the server's hard drive), and delivers it back to the customer's table.