Mirror universe
(coexisting on another dimensional plane)
(coexisting on another dimensional plane)
The T-90 tank was a type of tank used in the mirror universe on Earth during that planet's late 20th and early 21st century. (ENT: "In a Mirror, Darkly", "In a Mirror, Darkly, Part II")
Although not mentioned by name, a T-90 tank appeared in the alternate history opening credits of the mirror universe episodes "In a Mirror, Darkly" and "In a Mirror, Darkly, Part II", indicating that it was manufactured and used in that universe.