hort for Operational Amp, a circuit component used in all sorts of equipment. Though they are technically considered amplifiers they are quite often used in circuits that do not obviously "amplify" signals. Examples would be equalizers, crossovers, compressors, mixers, microphones, keyboards, effects and many, many, many more (the list is endless). Op amps acquired their name from early uses in analog computers (computers perform operations, get it?). They can exhibit very high gain and are extremely easy to build into audio circuits. Nowadays they are available in integrated circuit chips, each of which may have many op amps inside. In some cases they are literally a dime a dozen.