GABA is "gamma"-Aminobutyric acid (γ-Aminobutyric acid). It is a neurotransmitter in the central nervous system of mammals. It is an "inhibiting" neurotransmitter. Normally, when a neuron receives an impulse, it will make the signal stronger. In the case where there is an "inhibiting" neurotransmitter, the cell will no longer get the impulse, and the signal as a whole will be weakened.