The idea of concentrations and gradients within them is important when understanding the movement of substances across cell membranes.
When sucrose is dissolved in water:
The more particles there are in a certain volume, the more concentrated those particles are.
A solution with a low solute concentration has a high water concentration, and a high water potential. Pure water has the highest water potential.
A concentration gradient exists when there is a region of high concentration leading to a region of low concentration: