Apparently we are talking about the same thing, but in reality there are differences of historical nuance.
Some armies, such as the United States, call tank, or more specifically main battle tank, the tank, a name that was originally used during World War I to designate armored vehicles.
Unable to break the enemy lines, before whose barbed wire and machine guns hundreds of thousands of soldiers died, the British decided to build a land battleship which, to keep it secret, they called water tank for Palestine.
It was then that tank became synonymous with what is, correctly, nothing more than the current and most powerful version of the old tank.