Last I checked, anything with RWD or 4WD, a frame, and a bed is a pickup truck (no, Honda Ridgeline is not a truck! It's a FWD Unibody pavement pounder)
A Ford F-350 Super Duty is a pickup truck, just like a 1992 Toyota 1/2 Ton is a pickup truck. There's different sizes.
So, while a 4Runner is not a pickup truck, since it has no bed, it's just a light truck. It's like an enclosed truck. It still has a frame, it's still RWD based, it's still got a large cargo area.
SUV's are trucks, based off of truck platforms (IE: Light Truck: 4Runners, based on Tacoma, Xterras, based on Frontier, Old Exploders,based on Ranger. Truck: Sequoia, based on Tundra, Expedition, based on F150, Excursion, based on F250, Pathfinder Armada, based off of Titan, etc). They are not to be confused with Crossovers, which are based off car platforms. (IE: Mazda Tribute/Ford Escape/Mercury... Mariner or something, Toyota Highlander, Toyota Venza, Toyota RAV4, Honda CR-V, Honda Pilot, the list goes on... these are just prime examples)