Hey Hawk,
Clipping as actually when the receiver is asked to produce more power than it can cleanly produce. In the case of clipping, the root cause is the receiver, not a weakness in the speaker. Specced to handle 400 watts, the VP150 can probably actually handle much more power than your receiver is capable of 'cleanly' producing.
If you turn up the volume to the point where the speaker needs to draw more power than the receiver can produce, then the receiver tries to oblige but the effect is that the top and bottom of the frequency wave gets "clipped" off (thus the term "clipping") because it's hitting it's limits at that point in the sine wave. The result is a squared off wave and this type of distortion gets increasingly audible the more you push it and eventually becomes damaging to speakers.
A regular sound wave. 
.
A clipped sound wave. 
Most modern receivers will shut themselves down before too much damage occurs but there is always this inherent danger if you push volume levels too high.
