The distinction is a little iffy -- from what I understand, a sorcerer is like a wizard without the formal training. A wizard means you're in some way recognized as one by the White Council -- there's mentions of trials and such; I think Jim's said that one basic guideline is they're able to do everything between evocation and thaumaturgy. They might have a specialization and/or suck at one or two, but they have the capability of doing it all.
Sorcerer is a specialist, typically of something destructive like curses or burning things. IIRC it's a bit of an insult to use the term for focused practitioners who aren't solely about hurting people.
