What is TSS - Tangential Signal Sensitivity?

Tangential Signal Sensitivity (TSS) is the lowest input RF power level (in dBm) for which the detector will have a Signal-to-Noise Ratio (SNR) of 8 dB at the output of a test video amplifier. It is used to specify the noise performance of a log amplifier and also helps in defining the lower limit of the input dynamic range of a log amp. The TSS is based on the video bandwidth, detector figure of merit, and the video amplifier noise performance.

Another way to define this would be that TSS is the minimum pulsed input signal that causes an output signal that is equal to or tangential to the output noise peaks.