What does "ii-V-I" mean?

I've seen something similar written to this around a lot, but I'm not sure what it means. Help please?
lower case roman numerals mean minor chords, so thats a minor-2nd, 5th, 1st progression (thats the proper word for it).

ie: Dm, G, C (in the key of C) or Gm, C, F (in key of F)
I think I'm getting the idea. What do III, IV, VI, VII, etc. mean?

Edit: tonic means root note (I think), what do the others mean? Still a little lost.
Last edited by andersoncouncil at Sep 13, 2007,
I - Tonic.
II - Supertonic.
III - Mediant.
IV - Subdominant.
V - Dominant.
VI - Submediant.
VII - Subtonic.

Each refers to a scale degree - in C Major, the notes would be labelled..

I - C (CΔ
ii - D (D-7)
iii - E (Esusb9)
IV - F (FΔ#11)
V - G (G7, Gsus)
vi - A (A-7, A-7b13)
vii° - B (Bø

Your progression, is a ii - V - I progression, thus you get D-7 (ii) - G7 (V) - CΔ (I) (Dm7 - G7 - Cmaj7).
they are roman numerals representing the degrees of the major scale

I - ii - iii - IV - V - vi - vii(dim)
1st to 7th with their case representing Major or minor.

the order, if my memory is good enough -

I tonic
ii supertonic
iii mediant
IV sub dominant
V dominant
vi sub mediant
vii leading tone

somebody may confirm those

EDIT - oh... read johns post :-)
DOUBLE EDIT - where do i get the maj7 and dim symbols?

John: I get them from the Character Map on Windows.