Umbilicals are wire managers that help manage the gangs of wires that may travel from the floor to your desk. They are particularly useful if your desk is freestanding in the workspace and the otherwise unmanaged wires would form a tangly mess. Above is the Knoll wire manager.
They typically look like a series of vertebra usually divided into 2-4 sections, and wieghted at the floor to prevent them from moving around. If you have a floor outlet it usually would park right next to it, and you will notice that many of these have a ring shaped base meant to straddle an outlet. Now you can keep your power in one compartment, phone and fax line in another, and network (if you still have a wire for that one) in a third.
If this makes sense for you, and going to a big furniture company for one of these is not practical then Doug Mockett offers several configurations.