As you may have noticed, there are three mechanical arms reaching from the fixed umbilical tower to the Delta IV Heavy rocket and Orion spacecraft at the pad. The arms hold a series of lines and cables that are connected to the rocket during the countdown.
For Orion, the lines provide power and atmosphere control for the spacecraft inside the fairing. The arms connecting to the rocket hold lines that perform a number of functions including carrying gaseous hydrogen fuel away from the rocket. These devices would obviously be close to the rocket as it lifts off, so at the last moments of the countdown, they will revolve away from the Orion and Delta IV Heavy as they begin their climb toward space. That movement is what gives the mechanisms their name: swing arms.