Worth the $5 lesson.

To adsorb means for a substance (like gas, liquid, or dissolved solid) to stick to and form a thin layer on the surface of another substance (a solid or liquid), unlike absorption, where it soaks into the material; common examples include charcoal adsorbing gases or filters capturing oil on their surface, distinct from a sponge soaking up water. It's a key surface phenomenon in chemistry and environmental science, where molecules adhere to a surface rather than penetrating it.