Is there any opposite name for Decibel? According to definition of decibel it’s “logarithmic unit of measurement used to express”

So in audio we often convert linear value from range 0 to 1 to logarithmic scale for example like that:

double result = 20.0 * log10(valueInRange_0_1);

(of course we need to menage situation when valueInRange_0_1 = 0, but leave it now, it’s not the case)

So for example for valueInRange_0_1 = 0.5 result will be about -6 and we can call it “-6 decibels”.

But the question is how we can call valueInRange_0_1 = 0.5:

“0.5 OF WHAT” ?

I know in audio we can call it “0.5 gain”, or “0.5 of linear value”. But is there any general term to use as opposite to decibel?
Most of the time, it's the ratio of a physical quantity to a reference. The reference can either be an industry standard (Example: dBSPL, dBm, dBu etc.) or some other suitable quantity (Example: voltage at the input of a filter). 

"Physical quantities" in audio are things like pressure, volume velocity, particle velocity, displacement, voltage, current, force, etc. (20 log) or sometimes also power, energy, or intensity (10 log).

For example: a microphone measure "sound pressure" as a physical quantity and to make it logarithmic you use

$$P = 20 \cdot log_{10} (p/p_0)$$

where $p$ is the original sound pressure, $p_0$ a suitable reference pressure, (20 micro Pascals is industry standard) and P the resulting sound pressure level in dBSPL.

Taking a ratio is very important, since it also takes care of the units. In digital signal processing, you often just deal with numbers (without units), but a proper choice of reference is still important. Typically choices are either digital full scale, some suitably calibrated physical quantity or just simply "1" . The reference is important: a dB value without a well defined reference (implicit or explicit) is meaningless.