Ken teaches me a lot. Long time pilot and military man, flight operations manager, ace photographer, computer expert, ham radio operator, eagle scout, the guy is a veritable encyclopedia.
When we were out shooting the other day he said something to me and I said "Roger that." I thought I was assenting, he told me it meant nothing of the kind. "Roger", according to my friend, simply means "I hear you, or received." "Wilco" means I will comply. So "Roger wilco" means I hear you and I will comply.
These radio communication terms are called procedure words or prowords. They derive from early Morse code transmission. The NATO communications manual ACP-125 contains the most formal and perhaps earliest modern glossary of procedure words. They are still used by many organizations including the Civil Air Patrol and Coast Guard.
Another proword is over. It means my transmission to you is complete and I expect an answer. You never say over and out. Out means my transmission to you is finished and I require no response. There are many more of these words. You can see a good glossary here.
And the phrase 10-4? Where did that come from? It is one of the ten codes, or radio signals, invented by the Association of Public Safety Communications Officials (APCO.) It means okay. These codes are the brainchild of Illinois State Police Communications Director Charles Hopper for use by the police in their radio transmissions in 1937.