A web host is a dedicated space for serving content on the world wide web. It typically consists of a computer, or chain of computers referenced as a server. These servers hold all of the files necessary for running a website and are typically the final location of a domain request before returning content to your browser. There are hundreds of companies dedicated to hosting web content, and typically vary by their offerings on-top of their servers, including: security, application integrations, redundancy, speed, and more.
There are many different hosting plans, though they typically boil down to three different types of hosting. First is called shared hosting, which is basically a single server with multiple websites being hosted within. This is great for small and low traffic websites, and typically the cheapest plan. Next is a virtual private server (VPS), which is a dedicated space on a server with greater flexibility and control. This is typical of a growing website with greater backend customization requirements. And finally a dedicated server is a completely isolated server specifically created for a single website. This is the most expensive of the three and is primarily used for high-traffic and high-requirement websites.