Any type of sauce that is free of propitiatory ingredients and procedures. In order for a sauce to be deemed as opensauce, he 'sauce code' must be freely available under a GPLv3 licence for all to see.
Person One: Hello; welcome to Burger King, how can I help you?
Person Two: Hey, could I please get a whopper with cheese, without pickle, onion or tomato?
Person One: Sure, that'll be five dollars.
Person Two: Could I please have that with ketchup that conforms to opensauce standards?
Person One: Sure that'll be three dollars. I should note that you'll have to build it yourself, and Burger King is not responsible for anything you do. Oh, and it tastes like cow shit.