U,V,W are the norms for 3 ph wiring...
Imagine a triangle, the corners being marked as U,V and W.
One winding would be U1-U2, second would be V1-V2, etc...
So for Delta, the connections would be U1 to W2, U2 to V1, V2 to W1...
Star connected, the 2's would be connected and phases applied to the 1's