Trigger foods are foods that set off a binge or derail your diet. They're different for everyone, but common ones include cookies, cereals, peanut butter, chips - I could go on and on and on...
The Core plan warns about trigger or red light foods. They can be anything that will set you off to eat more than one serving. Even a Core food could be a trigger food. Even if it's Core, you should try to avoid it if you don't have any control with it. I have to be careful with avocado and edamame.