Microstate
A specific detailed microscopic configuration of a thermodynamic system, specifying exact positions and momenta of all constituent particles.
Governing formula
S = kB ln Ω
SI unit
N/A
In depth
Statistical mechanics assumes all accessible microstates corresponding to a given macrostate are equally probable in equilibrium (Fundamental Postulate).
Examples in the real world
Specifying 3D spatial coordinates $(x_i, y_i, z_i)$ and momentum components $(p_{xi}, p_{yi}, p_{zi})$ for all $10^{23}$ gas molecules in a container.