What is Mass concentration?

Example 26.2 (Sugared water)

$20\,\mathrm{g}$ of sugar are dissolved in water, and the solution is made up to $0.50\,\mathrm{L}$. Its mass concentration in sugar is $C_m = 20\,\mathrm{g} / 0.50\,\mathrm{L} = 40\,\mathrm{g}/\mathrm{L}$. Any part of it has the same concentration: a glass of $0.20\,\mathrm{L}$ of it holds $40\,\mathrm{g}/\mathrm{L} \times 0.20\,\mathrm{L} = 8.0\,\mathrm{g}$ of sugar.