Sisig is a Kapampangan (language in Pampanga province) term which means “to snack on something sour”. It usually refers to fruits, often unripe or half-ripe, sometimes dipped in salt and vinegar. It also refers to a method of preparing fish and meat, especially pork, which is marinated in a sour liquid such as lemon juice or vinegar, then seasoned with salt, pepper and other spices.
Sisig also refers to Sizzling Sisig, a Filipino dish made from parts of pig’s head and liver, usually seasoned with kalamansi and chili peppers. The dish is said to have originated from locals residents who bought unused pig heads from the commissaries of Clark Air Base in Angeles City, Pampanga. Pig heads were purchased cheap since they were not used in preparing meals for the U.S. Air Force personnel stationed there. An alternate explanation of its origin is that it is but an innovative variation on an older recipe, which is pork ears and jowl, boiled, chopped then marinated. (From: Wikipdedia)