osmosis is a phenomenon in which water crosses a barrier that divides two different media, flowing from the medium with a lower concentration of solutes to the medium with a higher concentration of solutes. This is to reach homeostasis or equilibrium in which the concentration of solutes is equal in both media.
While osmosis is the movement of water through two media, diffusion occurs in a single medium in which the solute is distributed in equal parts throughout this medium, an example would be a drop of dye that is distributed in a glass of water until the water is blue in its entirety.
Finally, absorption is a concept that varies depending on the system being discussed, but the simplest concept is the process in which a fluid is absorbed by an object that can be hydrated, for example, a sponge absorbing water.