Adsorption isotherms describe how molecules adhere to a solid surface at a constant temperature. They illustrate the relationship between the amount of adsorbate (the substance being adsorbed) and its concentration in the surrounding phase, typically a gas or liquid. Common models include the Langmuir and Freundlich isotherms, which help predict how much of a substance will be adsorbed under specific conditions. These isotherms are crucial in various fields, including environmental science, catalysis, and material science. By understanding adsorption behavior, researchers can design better filters, catalysts, and materials for applications like water purification and gas storage.