I hear people talking about these when reffering to textures. What are they? Thanks!

not sure, I use U and V which is simply mapping a triangle with textures
example:
pt: 0,0,0 u = 0, v = 0
pt: 0,1,0 u = 1, v = 0
pt: 0,1,1 u = 1, v = 1
pt 0,0,1 u = 0, v = 1

that will map out a quad with a texture

S = horizontal texture coordinate
T = vertical texture coordinate

U = horizontal texture coordinate
V = vertical texture coordinate

weird, eh?

Thanks!