A term that describes a person who wants to be from another racial/ethnic background so much so that they act like they are that from that background, very stereotypically. They also view their perceived culture as superior to others even compared to their own actual background. Ruck is also the portmanteau of the words racial and cuck.
David: Hello, my fellow whites. How's it hanging?
Tom: David you are such fucking ruck, you aren't white you are mexican.
David: Please, let me have this please...
Military term refers to a ruck sack which is another name for a back pack. May also refer to all of ones personal web gear. To "ruck up" is grab your gear and go!