A stage is a specific, self-contained section of a cascaded circuit that performs a single operation on a signal before passing it to the next block. In an audio amplifier, for instance, a weak signal might pass through a preamplifier stage, a filtering stage, and a final power output stage. Isolating circuits into stages helps designers manage gain, impedance matching, and noise incrementally.
Heard on the job
Probe the output of the second gain stage and see if the signal is clipping there before it reaches the final driver.