What do peak-to-valley and mm/µV mean?
Peak to valley means the highest point of the signal to the lowest point. It's a little like peak-peak except that it implies a DC bias so that the "negative peaks" don't cross 0V, so valley is a better name for them.

mm/µv means millimetres per microvolt, or metres per millivolt. What THAT means depends on context you haven't given us, but for example, mm may refer to the signal amplitude on the display of a REALLY SENSITIVE oscilloscope (or an oscilloscope driven from an amplifier).