word-forming element, especially in scientific compounds, meaning "life, life and," or "biology, biology and," or "biological, of or pertaining to living organisms or their constituents," from Greek bios "one's life, course or way of living, lifetime" (as opposed to zoe "animal life, organic life"), from PIE root *gwei- "to live." The correct usage is that in biography, but since c. 1800 in modern science it has been extended to mean "organic life," as zoo-, the better choice, is restricted in modern use to animal, as opposed to plant, life. Both are from the same PIE root. Compare biology.
1920, in the electronics sense, "the return of a fraction of an output signal to the input of an earlier stage," from verbal phrase, from feed (v.) + back (adv.). Transferred use, "information about the results of a process" is attested by 1955.
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Definitions of biofeedback from WordNet
a training program in which a person is given information about physiological processes (heart rate or blood pressure) that is not normally available with the goal of gaining conscious control of them;