dominant thirteenth- chord V with an extra 7th, 11th and 13th- so say we're in C major, then the dominant is G, then on it you have your regular B, D, then F (7), A (9), C (11), and E (13), but it only works if the interval is of a 13th in the chord, ie. you can't put the E in the same octave as the original G or it just becomes the interval of a 6th.
then when you're writing it out in 4 parts you only write the tonic (ie. G), the 3rd, 7th and 13th.
i just wanted to feel really knowledgable just then! i have no idea what a quatral chord is...
anyway yeah, it's amazing how much there is in music- i love how incredibly logical it is!! and i've barely learnt any of it, can't wait til i can take an analysis elective cos it's the bomb!!