Facebook Connect is a solution for integragrating a website with a user's Facebook account. This most simple use for Facebook Connect is for an easier registration system. With millions of people already on Facebook, it makes registering on a new website a breeze since all the end user needs to do is log in via Facebook. With the barrier to registration lowered, this opens up the site for more social features.
In addition to simplifying the registration process, Facebook Connect allows the website to extend some social networking features onto their site, thus making it easier to share content through Facebook.