It means that its response to incoming signals has a fast rise time. This requires wide bandwidthe--flat response at least to 60KHz and preferably 150KHz or more.
If you were to look at a test report of an amp or preamp that shows both frequency response curves and square wave response (several Stereophile tests do), you'd find that there is a correlation between wide bandwidth and how square the square wave is--in other words, how immediate the response to incoming signal is. This is speed, and it's what is meant by a fast component. Fast components have sharper transients and generally more space between the notes and therefore more clarity.
