What is the difference between a truck and a SUV?

What is the difference between a truck and a SUV?
the only major differences are SUV's are typically four door vehicles and they usually come with four wheel drive. its rare to see an SUV without four wheel. Trucks can get (from factory) stronger frames such as with F-350 or 3500. these frames aren't used on SUV's. the largest frame ive seen was a 250 or 2500 frame on excursions and suburbans. and obviously, SUV's are completely enclosed as where trucks have a 6 or 8 foot bed.