Assuming the thread is still about, what do beginner, intermediate and advanced mean, then it is subjective, i.e. meaningless, and Pierre is right not to offer an answer.

Maybe the best answer is that it all depends on the teacher/examiner (most of what follows tries to investigate that idea, although I have been editing it, and it is now incoherent): -

The old ABRSM books have lower for grade 4, higher for grade 5, intermediate for grade 6 (the back end of suzuki 4 perhaps), and advanced for grade 7 up.

I think more modern ABRSM books just have beginner for grades 1-3, intermediate for grades 4-6 and advanced for grades 7&8?

When I was teaching myself CG, my aim was just to sprint as fast as possible to grade 6 because pieces below that level all tend to be found in dull compendia, but at grade 6 you start to get books of music by individual composers, and that mattered to me.

With the violin I am being a lot more patient because technique is everything, and I am following a strict ABRSM route.

The terms tend to crop up in situations where a subject is popular and a teacher wants a max class size of, say 10, but 30 students apply. The teacher then says, OK, we'll have three classes, beginner, intermediate and advanced. You decide which you are. Problem is, in that situation the tendency is for people to aim for the toughest class they think they can cope with because they don't want to pay their money and get nothing out of it, and because they hope they can get into the swing of things quickly and not look out of place. The teacher could audition everyone, but that might lead to disappointment. It happens a lot in languages. I've been to advanced classes where beginners hold everyone else back.

Maybe none of this helps, unless you extrapolate and try to identify yourself and your needs better. Or maybe the ABRSM should be trusted as one of those crusty old English institutions, and you should look at their website and acquire old materials on EBay or from charity shops?

AndrewH said when I learned the Telemann viola concerto, I thought I was an advanced player. That bubble burst rather quickly when I started to move up to stronger community orchestras and I found out that the Telemann concerto was considered a lower-intermediate piece. 

That's very interesting. I'm tempted to buy a viola solely to learn that piece. My teacher is a violist. Ill ask her what she thinks of the Telemann.

The only thing I'd add is that sometimes pieces are graded according to length as well as difficulty, so that, even if not technically difficult for an orchestral performer who has tons of stamina, a piece (i.e. the Telemann) might be beyond a less experienced player who does not yet have that stamina.

We have the same situation in Classics - Homer's Greek's technical level is low - what you might achieve at school by the age of 18, although admittedly it is also vocab-rich. But his 30,000 lines of poetry (18,000 in the Iliad and 12,000 in the Odyssey) require stamina and speed or you'll be old before you reach the end.