Impulse Responses
almost like a sampled Room or Hall. It's made as it's name says: Loudspeakers send out one short Impulse of Noise which is "recorded" by microphones and that one is used in those Convolution Hall Plugins like SIR, Space Designer,Rayverb etc.
find lots of Impulse Responses here Impulsantworten
deutsch: Impulsantworten..