Gain
Gain or GAIN may refer to:

Science and technology
Gain (electronics), an electronics and signal processing term
Antenna gain
Gain (laser), the amplification involved in laser emission
Gain (projection screens)
Information gain in decision trees, in mathematics and computer science
GAIN domain, a protein domain
Learning rate, a tuning parameter in stochastic approximation methods, also known as gain

Health
Primary and secondary gain, psychological mechanisms that may underlie an illness
Global Appraisal of Individual Needs, a set of psychological assessment instruments
Global Alliance for Improved Nutrition, a Swiss Foundation working in the field of malnutrition
Generating Antibiotic Incentives Now, a piece of American legislation

People
Gain (singer), a South Korean entertainer
Gain, anglicised form of Indian surname Gayen

Other uses
Gain (accounting), the increase of net profit
Gain (novel), a novel by American author Richard Powers
Gain (EP), an album by Sadie
Gain (detergent), a brand of detergent
GAIN Capital, a US-based forex trading company
Greater Avenues to Independence program, a precursor to the American CalWORKs welfare program

See also
Gein (disambiguation)
Gayn (disambiguation)
Gane
Gian