Sub-species of freelance journalist

Apparently there are two types of freelance journalist out there: casual and contributors. That's the first time I have heard about that disctinction, so can anyone enlighten me a bit more?!

It would be useful to know more if we decide to go into freelancing of course. But I also know you really need to have worked as a paid staff, gained the right skills and experience, networked your way around different magazines and newspapers, have great contacts for your commissions and earned yourself a reputation as a good journalist. No small feat...