Molecules of a substance are able to move between cells. What are the two main processes by which this occurs? What is the main difference between these two processes?

Within cells the two main forms of cellular exchange are diffusion and osmosis. These two terms can sometimes be mixed up as they both mean "the movement of molecules of a substance from an area of higher concentration to an area of lower concentration." The difference between the two processes is that where DIFFUSION is just the movement of molecules of a substance from an area of higher concentration to an area of lower concentration; OSMOSIS is specifically the movement of molecules of WATER through a SELECTIVELY PERMEABLE MEMBRANE from an area of higher water concentration to an area of lower water concentration.