What is per pixel lighting and shadowing?

Greetings, Mr. Cucumber. We''ve been expecting you...

Ok. Normally, lighting is done on a per-vertex basis. This
means that if you have a triangle, its colour is determined by
the amount of light hitting the vertices. Now, for small
triangles, this can be adequate. But, lets say you have a huge triangle, (or any shape), the size of the screen. If we shine a spotlight in the corner, like a really ickle one, instead of lighting that
teeny corner, the lighting affects the WHOLE triangle. This
produces innacurate results, as the level of detail isn''t to hot.
Also, if that spot-light shone in the centre of the screen,
instead of lighting a nice spot in the centre, no lighting would
be used, as none of the vertices fall inside the cone.

Now, with per-pixel lighting, the triangle is lit on a per-pixel
basis, not a per-vertex basis. It is a lot more accurate, as
each individual pixel is lit, not each vertex.

That probably didn''t help.

Actually it helped me a lot.
I Understand it now, it was what I guessed it was.
Thanks