Suspended animation, or cryogenic stasis, was the temporary cessation of a life form's vital functions, often used to transport individuals from one time period to another without ageing.
In 1901, Torchwood Three placed Jack Harkness (who had been buried alive since 27 A.D.) in cryogenic suspension so he could return to the 21st century without crossing his own time stream. (TV: Exit Wounds) In 1918, they placed Tommy Brockless in cryogenic suspension so that he could one day close a fracture in the Cardiff Space-Time Rift. (TV: To the Last Man) In the 21st century, Jack placed his brother Gray in cryogenic suspension after chloroforming him when he threatened Cardiff and fatally wounded Jack's teammate, Toshiko Sato. He planned to keep Gray frozen indefinitely until he could find a way to sort out the anger his brother harboured towards him. (TV: Exit Wounds) However, the Torchwood Hub was destroyed when a bomb implanted inside Jack detonated. It is unknown if the cyrogenic chambers of the Hub survived the explosion. (TV: Children of Earth: Day One)
Davros was sentenced to be placed in suspended animation as punishment for his crimes. (TV: Resurrection of the Daleks) Tranquil Repose placed dying millionaires and politicians in suspended animation until cures for their conditions could be found. (TV: Revelation of the Daleks)
Abigail Pettigrew was cryogenically frozen by Elliot Sardick against a loan of 4,500 gideons to her family. She suffered from a fatal disease that would soon claim her life unless she remained frozen. Her family kept her in this state, hoping a cure would be found for her condition. She remained frozen past Elliot's ownership and was passed down to his son, Kazran Sardick. The Eleventh Doctor woke her to calm a sky shark hunting himself and a younger Kazran by singing to it. The Doctor went back in time to alter Kazran's past when he refused to let a passenger ship in peril land in Sardicktown. He continued to visit Kazran every year at Christmas Eve, waking up Abigail each time. Abigail's life expectancy was limited to a very small number of days estimated by a counter on her stasis pod, which fell by one each time she was removed from cryogenic freeze. Though Kazran and Abigail fell in love with each other, her counter ran down to one final day, which he withheld until he became an old man for a last outing with her on Christmas Eve. (TV: A Christmas Carol)
Millions of years later, in the what the humans of that era call the 57th Segment of Time, the human race are miniaturised and placed in suspended animation on the Ark to survive the long voyage to Refusis II. (TV: The Ark)
The Seventh Doctor once spent unspecified millions of years in a coma, frozen within a block of ice. Though his clothing had mostly rotted away over the years, his body survived and he recovered fully. (AUDIO: Frozen Time)
Vassarian suspended himself in the Eternity Cage to the point when he began to regenerate. He was badly injured and decide to use the Cage to hold himself in stasis until help arrived. (AUDIO: The Eternity Cage)