Acronymic for Hyper Text Transfer Protocol, HTTP is the protocol used to request web pages (and other files and resources) from web servers, and otherwise exchange data back and forth using web browser applications.
It is possible (and useful) to troubleshoot HTTP servers using telnet - see Daemons, testing via Telnet for a simple example using the GET command. (Other basic HTTP commands include PUT and POST.)
HTTP servers available via the ports tree include Apache, Lighttpd, and thttpd, among many many others. Currently, Apache and Lighttpd are used and recommended by the maintainers of freebsdwiki.net.