The T-84 is a Ukrainian main battle tank (MBT), based on the Soviet T-80 MBT introduced in 1976, specifically the diesel engine version: T-80UD. The T-84 was first built in 1994 and entered service in the Ukrainian Armed Forces in 1999. Its high-performance opposed-piston engine makes it a fast tank, comparable to other modern MBTs with a power-to-weight ratio of about 26 horsepower per tonne.

A main battle tank (MBT), also known as a battle tank or universal tank, is a tank that fills the role of armour-protected direct fire and maneuver in many modern armies. Cold War-era development of more powerful engines, better suspension systems and lighter composite armour allowed for the design of a tank that had the firepower of a super-heavy tank, the armour protection of a heavy tank, and the mobility of a light tank, in a package with the weight of a medium tank. The first designated MBT was the British Chieftain tank, which during its development in the 1950s was re-designed as an MBT. Throughout the 1960s and 1970s, the MBT replaced almost all other types of tanks, leaving only some specialist roles to be filled by lighter designs or other types of armoured fighting vehicles.