A postgraduate degree is essentially any course that you may do after your undergraduate degree (i.e. post is the latin for 'after') so it's a course you do after your primary (first) degree. A Postgrad course can be done in anything and it doesn't have to be an unrelated course to your degree (i.e. I could have a BA in Geography, but I could go on and do an MA in geography or MSc in GIS). There are taught postgrads, these are; Master's, HDip's, P Grad Dip's, Dips etc... that have a taught (i.e modules and subjects with exams, and a research project) component, then there are Reseach post grads; MPhil, MLitt, certain types of MSc and of course PhD's that have an almost whole research component. This is the only way that I can answer your question, so I think you've got all the information right there.
A GRADUATE forum is for people who've completed any stage of their third level education and are joining the workforce and all of the issues that goes along with that.