Attached Link: What is UV all about ??

Not enough time for first question. (Someone will nail it for you) But the short answer on U & V is - "X" & "Y" were already taken.

UV's are called texture coordinates. They basicially are 2d coordinates where each vertex of a polygon should grab its texture from. Imagine your mesh (like the p4 nude woman) is divided into triangles with 3 vertices. For each vertex there is a UV texture point. The UV points are the position on the p4 nude woman texture map where the texture is located. For example, the triangles that make up the lips have UV coordinates that map onto the lips portion of the texture. If you look at the UV Map for the p4woman you'll see these triangles or polygons. When the system goes to render the triangle on the figure, it looks up the UV coordinates and takes that section of the texture map as the section. Now what UVMapper does is it allows you to rearrange the UV coordinates so the texture is as flat as possible to make it easier to draw on. In reality, UVs are percentages ie instead of saying the texture's corner is at 213,345 on a 512,512 map it will be 0.416,0.673 (41.6%,67.3%). This way you can scale the texture to 1024,1024 and it still works. Also, there is a W component which is actually the z component for 3d textures.