Pain

Pain was an unpleasant feeling experienced by organic beings in response to a stimulus that damaged the body in some way. (TV: The Gunfighters) Pain was often accompanied by autonomic responses. (AUDIO: The Movellan Grave)

Certain parts of the humanoid body were more sensitive to pain than others, such as immediately below the eye. The pain of a cigarette being extinguished in this part of the body was enough to successfully break the Eighth Doctor's self-induced trance. (PROSE: Endgame)

The Eternal of the same name was a personification of the concept. (PROSE: Set Piece)

While pain was generally considered unpleasant, to the point of the word "pain" being used generally to describe an unpleasant experience or person, (TV: The Caves of Androzani) and as such was often treated with painkillers, (TV: Exit Wounds) some enjoyed the sensation of pain, while still others enjoyed pretending to be in pain. (PROSE: Of the City of the Saved...) In a more abstract sense, the Twelfth Doctor believed pain to be "a gift", because "without [pain], we can't feel the hurt we inflict". (TV: Death in Heaven) Additionally, some cultures did not show as much care for those in pain. When a Patient complained of pain, a Mondasian nurse responded simply by turning its volume down. (TV: World Enough and Time) Ironically, however, the Cybermen spoke extremely negatively of pain and spoke almost pityingly of unconverted individuals for still having the capacity for it. (TV: The Age of Steel)

The Monks believed that pain was information. (TV: Extremis)

Pain was also something people felt during things such as Death of a Spouse, Parent or Sibling etc.