snr stands for signal-to-noise ratio. The actual signal to noise ratio of an impulse response measurement is estimated from the resulting response itself, and presented as the snr. For the calculations done from the Calculate menu, the estimation of the background noise level is done using the last 10% of the impulse response, and the accuracy thereby depends on this actually being a flat noise floor. This ratio is, however, not of much practical use in room acoustical analysis. The edr (effective decay range) is more useful.