Absorption is the phenomenon of uniform distribution of a substance throughout the bulk of the solid and liquid. It is a bulk phenomenon. For example, absorption of water into the bulk of a sponge.

On the other hand, adsorption is a surface phenomenon in which the molecules of a substance are distributed on the surface of the solid or liquid rather than getting distributed into the bulk. The substance which gets adsorbed is called the adsorbate and the substance on which adsorption takes place is called an adsorbent. The adsorbate remains on the surface of the adsorbent. For example, a chalk stick dipped in blue ink remains white from the inside when observed while it appears blue from the outside.