What does this equation mean?

Szilard reduced Maxwell’s population of molecules to the simplest case that still carried the paradox: a single gas particle in a box. An external agent measures which half of the box the particle occupies, inserts a partition, and lets the particle push a piston on the side it occupies, converting the result of that one-bit measurement into extractable work. Szilard showed that the demon’s ability to extract work was tied exactly to the amount of information it acquired in the measurement — one bit of information corresponds to a definite quantity of work, $k_B$ T $\ln$ 2 , where $k_B$ is Boltzmann’s constant and T is the bath temperature. This is worth stating as an equation because it is the single quantity that recurs across the rest of this history: