Gamma-aminobutyric acid (GABA) is a naturally occurring amino acid that works as a neurotransmitter in your brain. Neurotransmitters function as chemical messengers. GABA is considered an inhibitory neurotransmitter because it blocks, or inhibits, certain brain signals and decreases activity in your nervous system.
Merriam-Webster Online Dictionary
GABA (abbreviation)gamma-aminobutyric acid