Cohesion refers to the attraction between molecules of the same substance, while adhesion refers to the attraction between molecules of different substances. In other words, cohesion is the force that holds similar molecules together, while adhesion is the force that holds different molecules together. For example, water molecules are cohesive, which is why they stick together and form droplets, but water molecules also adhere to other substances, which is why water can "climb" up a narrow tube or stick to the surface of a leaf.
