Phantom Zone

The Phantom Zone, was a prison for all the criminals of the 28 known inhabited galaxies, criminals were exiled there because many of them had long life spans, were too tough to kill using normal weapons, prison bars or force fields wouldn't hold them, and they posed a potential threat to Planet Earth. Some criminals were sent to the Phantom Zone of only 40 years while others for life, however the majority of them ended up serving life sentences and their corporal bodies destroyed, making them Phantom Zoners or Wraiths, which both Kara Zor El and Clark Kent fought in the TV series Smallville. It was said that Jor El built the phantom zone out of compassion so that the prisoners could make some sort of life there despite the fact that there is no yellow sun and it is a windy dry black desolate desert like place. The Phantom Zone has appeared in the comics, Smallville and the Supergirl film, however it is mentioned in the Superman I and II films and General Zod, Ursa and Non are seen trapped inside from a glass square.

Known prisonners
General Zod General Zod (comics)

Clark Kent (Smallville)

Kara Zor-El (Smallville & Supergirl film)

Aethyr-Ka (Smallville)

Nam-EK (Smallville)

Faora (Comics)

Raya (Smallville)

Ursa (Superman I & II)

Non (Superman I & II

Slade Wilson (Smallville)

Drax (Legion of Superheroes)

Dax-Ur (Superman TAS)

Mala (Superman TAS)

Source
Phantom Zone article at the Smallville wiki