No matter what area of electronic design you’re involved with, op amps play a key role in the conditioning and amplification of analog or "real-world" signals. A list of op-amp applications could fill a page, but some of the more common examples are digital oscilloscopes and automatic test equipment, video and graphics computer boards, medical instruments, TV broadcasting equipment, aircraft displays and air traffic-control systems, automotive sensors, computer workstations, and wireless basestations.
The ideal op amp has both infinite gain and infinite bandwidth. But a real op amp has a number of different gains that are each finite, along with frequency-dependent performance (see "We Got Gain"). Moreover, gain and frequency are related through the multiplication of gain times bandwidth or the gain-bandwidth product (GBW), a constant. This frequency dependence of a voltage-feedback op amp is best illustrated on a Bode gain plot, a log-log response curve that shows how an op amp’s gain declines (attenuates) with increasing frequency. A Bode plot is an important tool for determining whether or not an op amp is suitable for a particular application.