When they talk about ripple, they're probably referring to the waveform coming out of alternator. The alternator is really a small 3-phase AC generating station. Three windings in it produce alternating current output that are 120-degrees out of phases. These outputs are fed through a rectifier block and the result is a waveform that has peaks and valleys but which always stays positive. As one phase maxes out and begins to drop in output, the next is rising and when the next one has a greater output than the falling one, the rectifier output follows it. The term "ripple" refers to the difference between the peak and valley voltages at the output of the rectifier. As a simple example of ripple at work, most who've installed aftermarket stereos have heard that annoying whine in the speakers... That whine is caused in part by the ripple nature of the alternator output (and bad grounding...)
Excessive ripple may mean that one winding of the alternator is open or that a rectifier has gone bad. In any event, if the diagnosis is correct, you're probably looking at a new alternator.