Pain (from Ancient Greek ποινή - poine) is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”.

Pain in animals, including humans, is frequently the result of nociception; activity in the nervous system that results from the stimulation of nociceptors. This activity is carried to the brain, usually via the spinal cord, and conveys information, without conscious awareness, about damage or near-damage in body tissues. Pain is the conscious experience of sensorial information and a feeling of unpleasantness that can manifest as a result of nociception. Neuropathic pain differs from nociceptive pain in that it involves damage to the nerve resulting in the sensation of pain. There is also central pain in which the pain is generated in the brain from some form of lesion, and which is the most difficult for medical professionals to treat. Occasionally pain may be psychogenic, meaning caused by mental illness; however this is exceedingly rare.

As a part of the body's defense system, pain triggers mental and physical behavior that seek to end the painful experience. It is also a feedback system that promotes learning, making repetition of the painful situation less likely. The nociceptive system may transmit signals that trigger the sensation of pain, it is a critical component of the body's ability to react to damaging stimuli and it is part of a rapid-warning relay instructing diverse organs and principally the central nervous system to initiate reactions for minimizing injury.

"Pain" is a song by the American band Jimmy Eat World. It was released as the first single from their 2004 album Futures and became their second #1 hit on the Billboard Modern Rock Tracks chart. The song was featured on Tony Hawk's Underground 2 and Midnight Club 3: DUB Edition. The 7" was pressed on clear vinyl.

"Pain" is the second single from rock band Three Days Grace's second album, One-X.

According to the band, the song is based on the pain and loneliness encountered on the road during their tours. The band describes this as when people are inches away from you, but you feel miles apart. They allow themselves to be immersed in pain and depression, while they try to listen to a voice that tries to help them break free of this pain.