In layperson’s terms, what is the difference between a “reverse proxy” and a “web server”?
In simple terms, you can think of a reverse proxy as an http server that is a middle man. For a simple case why you might use one. SSL/TLS can be a pain to set up in your web application code. So what you can do is write your web application and not worry about SSL/TLS certs. Then you can place a reverse proxy infront of it and configure the reverse proxy for SSL/TLS. This way your not dealing with that complexity in your code and someone else is managing it. From there, the reverse proxy takes requests and reroute them to your web application. My reverse proxy is exposed to the internet on port 443, when a packet hits it, it knows to rereoute the traffic to server running on my machine at localhost port 8080. You can also have a reverse proxy to have one singular ingress point for many web applications. The reverse proxy will know that requests for http://MyCoolWebApp.com go to localhost:8080 and http://MyOtherCoolWebApp.com go to localhost:8081.
Source: https://news.ycombinator.com/item?id=40520252
Reverse proxying is just one task that a web server can perform. Caddy also has a file server (directly serving files from disk or from some virtual filesystem), can write static responses, can directly execute code via plugins like FrankenPHP, can manipulate/rewrite/filter/route the request and/or response, etc. Just look at this list https://caddyserver.com/features