What does the R stand for in the ideal gas law (PV=nRT)?

The units of the universal gas constant $R$ is derived from equation $PV=nRT$. It stands for Regnault.
If
- the pressure $P$ is in atmospheres (atm),
- the volume $V$ is in liters (L),
- the moles $n$ is in moles (mol),
- and temperature $T$ is in Kelvin (K),
then $R$ is in $\mathrm{L}\cdot \mathrm{atm}/\mathrm{mol}\cdot \mathrm{K}.R$ has the value $0.082057\mathrm{L}\cdot \mathrm{atm}/\mathrm{mol}\cdot \mathrm{K}$ with the above units for the remaining variables.
In other scenarios with pressures of bars instead, you may also use $0.083145\mathrm{L}\cdot \mathrm{bar}/\mathrm{mol}\cdot \mathrm{K}$. However, temperature must always be in Kelvin (K), as $R$ uses units of $\mathrm{K}$.
There is a variation of the ideal gas law that uses the density of the gas with the equation
$PM=DRT$
where $M$ is the molar mass in $\mathrm{g}/\mathrm{mol}$ and $D$ is the density of the gas in $\mathrm{g}/\mathrm{L}$.