Bob and Cheater:
In audio, signal analysis, video, here are my definitions, of course open to your comments!
Noise floor is the measured RMS with no signal and the device terminated in desired Zo, eg place a 50 Ohm term on the BNC of a scope plugin, view the noise floor and measure RMS.
Signal to Noise Ratio: SNR:
Ratio of a standard or nominal signal level to the noise floor, eg a -10 dBm normal signal level and -90 dBm noise floor gives SNR 80 dB. Of course one must define the nominal signal level!
Dynamic range is the max signal level before a specified distortion eg 1% THD, or a certain 3rd order IM, to the noise floor.
In the same example above, for a -10 dBm nominal, the system has 5% distortion with a +15 dBm signal, thus the dynamic range is +15 (-) -90 = 105 dBm.