Planet 14

Planet 14, also known as Sol XIV or Planet Sigma Gamma 14, (PROSE: The Invasion) according to one account, was the fourteenth planet from Sol, inhabited by Cybermen. (PROSE: Iceberg)

History
According to one account, 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. (PROSE: Iceberg) They were driven away when the planet's own power was used against them, resulting in a catastrophic explosion. (PROSE: Scientific Adviser)

According to another account, Planet 14 was the Cybermen's home planet of Mondas earlier in its history, back when it was also known as Marinus. The Voord of Marinus quick-evolved the planet into Mondas and quick-evolved themselves into the earliest Cybermen. (COMIC: The World Shapers)

The Cyber-Planner told Tobias Vaughn that both the Second Doctor and Jamie McCrimmon had been on Planet 14 in unseen events prior to Vaughn's first encounter with the duo. (TV: The Invasion)