What is Microstates and macrostates?

Example 16.3 (A magnet of $N$ coins)

$N$ independent spins, each up or down: $2^N$ microstates. The macrostate “$n$ up” has multiplicity $\Omega(n) = \binom Nn$, overwhelmingly peaked at $n = N/2$ with relative width $\sim1/\sqrt N$. For $N = 100$: the all-up state is one; the balanced macrostate holds $1 \times 10^{29}$. For $N = 10^{20}$, deviations of even $10^{-8}$ in the up-fraction are suppressed by factors like $\eu^{-10^4}$: the system is at its peak, and what we call equilibrium is the macrostate with the most microstates.