Triscuit is the brand name for snack crackers, made by Nabisco, which take the form of square baked whole wheat wafers.
When Corey gets Meg started on the road to internet fame in"Girl, Internetted", Peter proposes celebrating with Triscuit Pizza, noting that the recipe is right on the Triscuit box and can be made with ingredients likely to already be in the house and ignoring Meg's inquiries into the taste. When she finally tries one for herself, she compares it to a tomato dropped in hay. Peter further compares it to a pizza made by a horse and suggests having a drink near by.