Definitions of Absorption and Adsorption.

Absorption

The process where one material is taken in by another. At a molecular and atomic level, the molecules of one material fill in the empty spaces between the molecules of the other material. An example of absorption is a paper towel picking up water.

Adsorption

The surface interaction between two materials where one material adheres to the surface of another. While the atoms of the materials bond to each other, they do not combine. An example of adsorption is paint on a wall. The paint molecules attach to the wall molecules but remain separate.