Balanced means that there are two signal lines, of opposite electrical phase and equal amplitude. Neither is referenced to ground. The most common balanced audio connector is XLR. (Unbalanced has one signal line referenced to ground.)
However, as you indicate, some XLR inputs and outputs are not balanced. (I just reviewed a preamp with an unbalanced XLR input and an XLR output that can be ordered balanced or unbalanced.) And, yes, pin1 is generally ground, pin2 is (+) and pin3 is (-) in the US.
However, as you indicate, some XLR inputs and outputs are not balanced. (I just reviewed a preamp with an unbalanced XLR input and an XLR output that can be ordered balanced or unbalanced.) And, yes, pin1 is generally ground, pin2 is (+) and pin3 is (-) in the US.