A tank was an armoured fighting vehicle.
When the Twelfth Doctor was having a party to celebrate what he believed would be his last days, he brought a tank to 1138. As a joke he claimed that he had bought it online for his fish, however the crowd didn't understand the reference. (TV:The Magician's Apprentice)
In 1942, Captain Ernst Wolfgang Spiegal threatened to have a tank destroy a schoolhouse with the children still inside if Professor Pierre Vedrun and the Third Doctor were not returned to him. (COMIC: Timebenders)
In 1958, Area 51 deployed a battalion of tanks to battle a horde of Viperox levelling the town of Dry Springs, Nevada after their leader, Lord Azlok, turned against Colonel Stark and broke off a deal to help defeat the Soviet Union in the Cold War with a bioweapon. These tanks were equipped with muzzle brakes to steady the aim of the cannon turrets. Nevertheless, the Viperox were agile enough to jump away from the artillery bursts and took flight to remain out of attack range. (TV: Dreamland)
The Kraals deployed tanks in their second abortive invasion of Earth. The capabilities of this tank were unknown, but Marshal Grinmal expressed concern that his forces would be subject to counterattack and ambush while on the M1, indicating that these vehicles were susceptible to human anti-armour weapons. (AUDIO: The Oseidon Adventure)
Daleks used an especially lethal type of tank that had a giant version of their gunstick weaponry outfitted to the mortar barrel. Like other tanks, it was apparently difficult to recover if it was disabled. One was left broken down and abandoned during the Siege of Trenzalore. (TV: The Time of the Doctor)