A web hosting is a computer where people store their websites. Think of it as a house where you store all your stuffs; but instead of storing your clothes and furniture, you store computer files (HTML, documents, images, videos, etc) in a web host.
More often than not, the term “web hosting” refers to the company that rent out their computer/servers to store your website and provide Internet connectivity so that other users can access to the files on your website.