default.master or custom.master

I was reading Stefan Goßner today regarding Site Master Page vs. System Master Page
That's was a master touch! Finally I know the difference between:

• "~masterurl/default.master": the page will use the site master page in the every page in the SharePoint site except Publishing pages
• "~masterurl/custom.master":  is used by Publishing pages

Now, what's Publishing pages?
Publishing pages. These are a special type of page. They require the Publishing Features of MOSS, and so aren’t in WSS. Publishing pages have a content type, and always exist in the Pages library of a site.

Additional reading:
Pages in SharePoint – Introduction