Adhesion is the process by which different substances stick together. This occurs due to attractive forces between the molecules of the materials involved. For example, when water droplets cling to a glass surface, it demonstrates adhesion, as the water molecules are attracted to the molecules in the glass. In various applications, adhesion is crucial. In the case of glue, it helps bond materials like paper or wood. Similarly, in biological systems, adhesion allows cells to stick to each other and to their surroundings, which is essential for tissue formation and healing processes.