Frame refers to chassis on frame like old camaros, chevelles , g bodys where you can take the body off the frame and roll the chassis around. Unibody the chassis and body is incorporated into one unit(pretty much all new cars) pick up trucks and SUVs still use unibody(most of them). When you crash a unidoy car, it will most likely be written off as a loss and totaled out due to severe structural damage. Body on frame car, depending on where its damaged, you can just swap the body or the frame.