Planet 14

Planet 14 (or Sol XIV) was the fourteenth planet from Sol, and was inhabited by the CyberFaction. (NA:  Iceberg)

Marinus, Mondas, and Planet 14 may have been the same planet (DWM: The World Shapers)

Location
Planet 14 may once have been in the Sol star system. The name refers to a time when there were at least fourteen planets in the solar system. This count of planets is likely to include Mondas, The Moon, Planet 5, Eris and Pluto as planets. (REF: Doctor Who: Cybermen)

History
The Cyberman species emigrated to Planet 14 from Mondas whilst it was drifting through space, where they evolved separately from the Mondans who remained on Mondas. Whilst on Planet 14 they pursued their goal of total Cyber-conversion. (NA: Iceberg, REF: Doctor Who: Cybermen)

Planet 14 was the location of an encounter between the Doctor and the Cybermen. The Cyber-Planner told Tobias Vaughn that the Cybermen had seen the Doctor on Planet 14 prior to their invasion of earth circa 1970s. (DW: The Invasion)