When two people talk to eachother spontaneously after a long period of being mad at eachother or something else that doesn't allow the two persons 2 talk to eachother. Refers to how when intelligence vessels are forced to not use their radios so that their position can't be discovered. When these vessels do use their radios, it is refered to as "breaking radio silence." Breaking radio silence usually does not reestablish the relationship between those two people, it just allows one of them to retrieve valuable information that they need.
Me: (to ex girlfriend) Hey, I know I'm breaking radio silence, but I forgot Todds cell phone number, so can I get that from you?
Ex Girlfriend: Yah, sure, it's (123)-456-7890.