Empathy is the capacity to understand or feel the emotions of another being from their perspective. It could also refer to a type of extrasensory perception in which one can directly detect the emotions of another; such an individual was known as an empath. Empathic powers were often associated with telepathy.
Species in which empathic abilities were normal included the Betazoids (and Betazoid hybrids), Deltans, Haliians, Lumerians, and Napeans. (Star Trek: The Motion Picture; TNG: "Encounter at Farpoint", "Man of the People", "Aquiel", "Eye of the Beholder") Gem's species was empathic, and further possessed the ability to transfer the wounds of others onto themselves. (TOS: "The Empath")