Simply put, a web interface is a frontend to a piece of software. The implications are great, and there is great potential for the use of them.

Common uses are for accessing databases (like a message board), or configuring hardware (like a Linksys Cable/DSL router). Web interfaces are every where. As you look up information on e2, you are using a web interface to access the database that actually contains all the nodes and writeups.
Y'know, if you log in, you can write something here, or contact authors directly on the site. Create a New User if you don't already have an account.