HAProxy is a reverse proxy and load balancer.
If you have a web server which already does HTTP and HTTPS, but you don't want to expose it to the internet (e.g. in a home server self hosting setup), you can proxy it through HAProxy.
frontend http bind *:80 default_backend upstream_http frontend https bind *:443 default_backend upstream_ssl backend claptrap_http server upstream 192.168.77.2:80 backend claptrap_ssl server upstream 192.168.77.2:443