That was in reference to DLMdD’s post. New users of the forum start at trust level 1, which means they can’t post any links to other sites. Once you’ve been active for a bit, you hit trust level 2, which allows links from certain specific websites. People active enough to hit trust level 3 (no small feat) can post links to any website whatsoever.
You can find more info on trust levels and other forum tools in the New Forum Guide.