Operational Amplifier - Avd - Aol Characteristic
dB by itself is a unitless ratio between a measured quantity and an established reference.  It's short for deciBel, where one Bel is defined to be a factor of 10 more power.  Thus, dB for power = 10*log(Measured/Reference)

Because we don't want to confuse our meters by having a different scale for power and signal (seeing that power ~= signal^2), we change the equation instead.  Using the properties of logarithms, we can convert log(x^y) into y*log(x) and get dB for signal = 20*log(Measured/Reference)

Given that information, you can easily convert between V/mV and dB.



As a side-note, there are lots of dB scales that imply the reference so as to use a single number to describe a measurable quantity.  For example:


0dBm = 1 milliwatt
0dBu = the voltage required to push 0dBm into 600 ohms** (~0.7746 volts rms)
0dBV = 1 volt rms
0dBSPL = 20 micropascals rms (rough lower limit of human hearing)
0dBA = 0dBSPL as measured on the same equipment but after a specific "A-weighting" filter (supposed to approximate human perception but grossly misunderstood and misused by the general public)
0dBFS = full scale, maximum level without clipping/distorting (actual level may vary wildly across different equipment, but this unit is very useful for signal integrity within each piece of equipment)
Etc.


** In case you're wondering, 600 ohms is roughly the characteristic impedance of old telegraph wires on wood poles.  Even though it seems arbitrary now, the unit has survived and continues to influence modern designs.



I'm not going to comment on "Aol" or "Avd" or other manufacturers' terminology without seeing datasheets.