Vacuum

A vacuum was an area that was virtually empty of matter. The most commonly known was that of space. Most life forms could not survive in a vacuum for very long.

Vacuum survival
There were, however, those who were able to survive in the vacuum of space indefinitely or for extended periods of time.

Time Lords could survive in a vacuum for limited periods. (DW: Four to Doomsday, TARDIS)

Daleks, (DW: The Parting of the Ways) Cybermen (DW: The Moonbase) Olympians, (DWM: The Life Bringer) Sensorites, (DW: The Sensorites) and Star Whales (DW: The Beast Below) were all capable of indefinite survival in a vacuum.

Wirrn could live within a vacuum for a period of years. (DW: The Ark in Space)

Toby Zed was able to survive in a vacuum whilst possessed by the Beast. (DW: The Impossible Planet)

Ahab, a member of an unknown humanoid race, was capable of vacuum survival. (K9TV: The Bounty Hunter)

Vacuum deaths
Katarina, (DW: The Daleks' Master Plan) Kirksen, (DW: The Daleks' Master Plan) Lynda Moss, (DW: The Parting of the Ways) Scooti Manista, (DW: The Impossible Planet) and the Chief Steward (DW: Voyage of the Damned) were all killed by vacuum exposure.

Varan was killed in the vacuum of space after the Marshal of Solos destroyed a wall of his Skybase, sucking Varan out. (DW: The Mutants)