explain "clipping to rail" or how op-amps distort

[nightingale]

i found a little bit on the net,
but i do not understand what "clipping to the rail" means in an audio op-amp circuit.

in my own experiments,
i have pulled lifted the connection to the clipping diodes on a few od-250 type circuit, and the post op-amp signal is not very clean.  i understand how the gain arrangement works in he loop, but i do not understand how the distorion is created w/out diodes in the loop.
it  crossed my mind that the soft distortion that i like of a rat/od-250 might be the allready distorted op amp signal, being clipped by diodes.
making pretty interesting harmonics?

i have heard people say that part of the rats sound comes from the distorting 308 chip.

thanks in advance,

[toneman]

OAmps all Use bi-polar supplies in one form or another.
If the signal voltage *and* voltage gain factor of OA exceed the
voltage of the powersupply, the signal is not *linearly*
amplified.  The signal gets as hi as the "rail", and then chops off.
Goes "flat"....It "rails out", "cilps".  
U could concevablly have only one  rail, say the positive,
doing the flattening.  The "clipping".
There R many tutorials on OAs on the web.
Look 4 ones that have a scope display.