It sound like an English football team, but it is actually a plugin for phpBB which allows you to share the users and theme of wordpress with phpBB. This may act as a good primer for this post. I wrote a post called Case Study: Adding A Forum To Your WordPress Blog about the various forum solutions for WordPress. This is possible via a WordPress forum plugin, bit these are often quite cumbersome and effect performace, or using Automattic’s own forum solution bbPress (Automattic are the company behind WordPress), but one of the leading and most robust forum systems is phpBB, people want an integration solution for that. The problem many blog owners have is that they want to share the user database of WordPress with a forum so they only have to administer one set of users.
UPDATE March 2011: Please see comments, it looks like this project has been closed down, I recommend SimplePress forum if you need a WordPress forum I came across a fabulous integration tool for WordPress and phpBB that I though I would like to share with you.