Osmosis is the result of diffusion across a semipermeable membrane. If two solutions of different concentration are separated by a semipermeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution.
Passive diffusion occurs along a concentration gradient from high concentration to low concentration. At the end, net movement of solute ceases, when the concentrations are similar everywhere. However, in the case of active transport the movement is happening against the concentration gradient from low concentration to high concentration.