Torture was the deliberate inflicting of pain, usually as a punishment against criminals or an aid in interrogations.
Jane Page was experienced in torture and thought it was a matter of technique. She explained that "eyes are good. Nails and teeth if you have the equipment. Breasts, if it's a woman." Her tip was to start with psychological torture as it got the victim in a better state. (PROSE: Falls the Shadow)
Jack Harkness was very experienced in torture from his Time Agent days, knowing just "where to apply the tiniest amount of pressure to a wound." He used this on Martin, who then told him what he wanted to know. (TV: Countrycide)
On Starship UK, the star whale transporting it was tortured to keep it moving. It was later revealed that this had been completely unnecessary, as the whale had wanted to transport the ship. (TV: The Beast Below)