Please explain clipping

I'll keep this short as I don't know the real technicals of it. Clipping occurs when an amp cannot drive the speaker to produce either really high or really low frequencies at the volume currently being asked of it. As far as my understanding goes, the amp responds by playing the signal at a lower frequency if it's clipping at high frequency, or vice versa. I'm still not sure if this damages the amp, so I tend to avoid it. The sonic difference would probably be a slight distortion of the sound at the upper and lower ranges. Most audiophiles appear to solve this problem by having an amp (or two) that will destroy the speaker long before it clips. It occurs to me I may be spouting crap here. Let's see if other, more knowledgeable folks describe it the same way...

Clipping occurs when one attempts to play music louder than the amplifier can deliver. It is characterized by extreme harshness and edginess in the high frequencies. The musical signal is literally 'clipped' off, resulting in a squared off signal. This square wave contains tremendous high frequency energy content which can only be dissapated as heat, usually in the tweeter, which can be damaged or destroyed. The amplifier can is also at risk as this excess energy, or current, can cause permanent damage by breaking down the P-N semiconductor barriers in transistors, diodes, and even capacitors. Speaker and amp fuses often do not provide adequate protection from clipping. If you must have loud music, get an amp with plenty of power and invest in efficient speakers.

Clipping occurs when an amplifier stage cannot supply either enough output voltage swing or current to the load. It is not really related to frequency, except that speakers often have a lower impedance in a certain frequency range (usually lower freq) and that is where the amp would tend to run out of gas when attempting to respond to a high amplitude (loud) passage in that range. This has been discussed in other threads at some length, you should search. The result of the rapid change in voltage / current when the limit is reached, is generally a high frequncy transient (spike) that typically would just be too much for the high frequency drivers, thus fried tweeters. Such damage is therefore usually the result of inadequate electronics rather than inadequate speakers. It has also been pointed out in another thread that clipping can occur in any preamp / amp stage and have sonic implications, but is usually thought about with respect to the final amp because of the physical consequeces. :)

Sf- Clipping is the inability of an amplifier to increase the amplitude of the input signal while maintaining the same waveform shape as the input signal. The peaks of a sinewave will no longer be round, but "clipped" flat. (This would be an example of severe clipping). Some amplifiers produce excessive amounts of distortion when this occurs and don't recover quickly or gracefully from clipping. Regrettably, without nearly limitless amounts of power, clipping is bound to occur sometimes. I seem to remember an MIT test where the reproduced sound of a pair of scissors still showed signs of slight clipping even with 2,000 watts available. Single-ended triode designs,and tubes in general, tend to handle this situation in a manner more pleasing to the ear, though they obviously have greater measureable distortion products than other topologies.
Hope this helps.

Sfrounds, Jcbtubes has given the best explanation. As an aside, there is evidence that between well designed amplifiers, the amp's recovery characteristis from clipping may be a key determinate in listener sound preference. Some amps go into short-term instability after clipping, while others seem unfazed.