You have a four cylinder engine.
I am not sure where the three cylinder thing came from, but there were some old Suburus that truly had very small three cylinder engines. They were tiny, more like motorcycles with four wheels and a canopy than actual cars.
Chrysler, Pontiac, Mazda and Ford (maybe others) have all experimented with small engines that "turn off" half the cylinders while cruising at low power, but a nice overdrive transmission was determined to be the best way to shut the engine down some, by simply reducing RPMs, in order to save fuel during times of low power needs.