Macrostates and Microstates
A macrostate represents a global (usually macroscopic) description of a system of particles, whereas a microstate speciﬁes, in greater detail, the individual states of the constituent particles. Many different microstates can correspond to the same macrostate, as in the case shown here of a system of 25 particles of two possible colors. Particles are distinguishable in a microstate; as each particle can be green or blue, there are possible configurations, but there are only 26 possible configurations for macrostates.
The number of possible microstates for a given macrostate is equal to , where is the total number of particles and is the number of particles in a given state, in this case represented with the color blue.
 Wikipedia. "Microstate." (Aug 6, 2011) en.wikipedia.org/wiki/Microstate_%28 statistical_mechanics %29.