Gamma-Aminobutyric Acid, usually abbreviated GABA, is a non-essential amino acid, used by your body as both a neurotransmitter and a metabolic/catabolic compound. It is found throughout many parts of the body, and is known to regulate neural growth, among other things. There are three different GABA receptors, called GABAA GABAB and GABAC. Most common GABAergic drugs act on GABAA, but some such as propofol and GHB act on GABAB. Your body makes GABA from glutamates. Nice to know all that MSG you're eating is good for something.
GABAergics are drugs that bind to the GABA receptors. These include many CNS depressants. Most of these drugs are known to cause memory blackouts. They cross-potentiate with each other and with opioids This is a common cause of fatal overdose so be careful when combining them.