Speaking topo map wise in as simple of terms as possible, Picture a ridge along the top of a hill. On the ridge there are two knobs, one to the left, one to the right. As you come down off the one knob { either one }continuing on and then ascending the other knob, the bottom point of your travel to the point you begin ascending the other knob is known as the saddle. It can be a wide expanse; a big ' U ', or it can be more pronounced, simply a ' V '. Picture viewing an actual saddle from a side-on view. That's the look, hence the name.