Super-heavy tank, also super heavy tank, is a semi-official term for any armoured fighting vehicle in the class beyond Heavy tanks. As such, they can most easily be distinguished from lesser vehicles by their very large size and mass.
Programs have been initiated on several occasions with the aim of creating an invincible vehicle for penetrating enemy formations without fear of being destroyed in combat; however, only a few examples have ever been built, and there is little evidence of any super heavy tank having seen combat. Examples were designed in World War I and World War II, along with a few in the Cold War.
As time went by tanks grew in size and mass, so what was a heavy tank at one point, became the equivalent of a medium tank a few years later. This is why it is impossible to set a specific limit for mass.
The first super-heavy tank was designed by the Russian naval engineer Vasily Mendeleyev who worked on the project from 1911 to 1915. The tank was envisioned to be invulnerable to almost all contemporary threats but remained on paper because of its high construction cost. Following the production of their first tanks, the British "Flying Elephant" was designed as a tank that would be resistant to artillery fire. Since mobility was more important than protection, and the tanks already developed were successful, work on the project was stopped. The German K-Wagen (Großkampfwagen) was a very heavy design carrying 4 guns and needing a crew of 27. Two of them were under construction when the war ended and both were demolished.
During World War II all of the major combatants introduced prototypes for special roles. Adolf Hitler was a proponent of "war winning" weapons and supported projects like the 188 tonne Maus, and even larger 1,000 tonne Landkreuzer P. 1000 Ratte and 1,500 tonne Landkreuzer P. 1500 Monster. The British & Soviets all built prototype designs similar to the Jagdtiger, but none of these saw combat as the need for such a weapon turned out to be extremely limited.
The idea of very heavy tanks saw less development after the war. Advances in armour technology allowed large tanks to stay in the approximate up to 65 ton range. Examples include Object 279 (Soviet Union) and T29 Heavy Tank (United States).
Further advances in armour technology have eliminated the need for super heavy tanks since the armour of late 20'th century tanks is estimated to be the equivalent of over a meter of Rolled homogeneous armour (the type of armour used before).
T-42 (Tank Grote or TG-V) - 100 tons with 107 mm main gun and four sub-turrets. Models and drawings produced 
KV-4 - 1941 project. A proposed 90–100 ton tank, carrying a 107 mm main gun and a 45 mm or 76 mm secondary; various layouts were considered, with the hull-mounted 107 mm and a 76 mm turret chosen as the final option. Feasibility stage only.
KV-5 - another Kliment Voroshilov series 100-ton-class tank design. Armed with the same 107 mm main gun in a large, KV-2-style turret, and two 12.7 mm machine gun turrets (one on the forward hull, one on top of the main turret); powered by two V2 diesels due to wartime lack of a 1200 hp engine. Project stopped due to Siege of Leningrad and cancelled without anything built.
Tsar Tank - A giant wheeled gun platform of 1914 which was abandoned because it was underpowered and vulnerable to artillery.
K-Wagen - 120 metric tons; two were nearly complete when World War I ended. Both were demolished.
T28 Super Heavy Tank - 86.2 metric tons; 2 prototypes built right after WWII; by layout it's actually a Tank destroyer; project cancelled. One can now be seen on display.