LR = Left or Right (meaning, either the left or right button will work in that combination)
UD = Up or Down (meaning, either the up or down button will work in that combination)
I know, its kind of annoying, especially in that its not consistent with the VC/LC USCM controls. Don't worry though, I my upcoming SA USCM update, these controls will be changed back to their VC/LC style equivalents.