Convolution uses several types of noise signal to record a particular space, whether it be a room, concert hall or guitar cabinet. When the noise is removed, all that's left is what that space sounds like. At least, that's the basic theory.
It's most common use is to create a reverb that is very realistic to the space it represents, by recording the impulse in that space. I've tried it myself, and the practical is a little more complicated.
This might help a little better than I can... Convolution reverb - Wikipedia, the free encyclopedia