Osmosis

Diffusion is when particles go from a place of high concentration to a low concentration, Osmosis is similar to diffusion but mainly for water.

Water concentration is the amount of other molecules most commonly sugars and salts, and how much is dissolved in the water. 
These molecules that dissolve in the water are named solutes, so if we take two beakers and fill both with water and then put one solute in the left beaker, and put 3 in the right beaker we would have a higher amount of solute concentration.

What matters is the amount of solute that is in the beaker, because that's what dictates the water concentration.