What phenomenon is called adsorption? What qualities of charcoal have determined its high adsorption properties?

What phenomenon is called adsorption? What qualities of charcoal have determined its high adsorption properties? Tell us about the use of charcoal in gas masks, in water filters, as a medicine, etc.

Adsorption is the absorption of a substance from a gaseous medium or solution by a surface layer of a liquid or solid.
After heating the charcoal and without air access, it retains the fine-pored structure of the wood and a large surface, these qualities of charcoal determined its high adsorption properties.
Due to this, charcoal is used in personal protective equipment for the respiratory system. The gas mask, developed by N. D. Zelinsky, saved many lives of soldiers in the First World War. By 1916, it was adopted by almost all European armies.
Also charcoal is used in medicine, because is able to remarkably cleanse the intestines and remove various toxins from the body; as well as in the chemical, pharmaceutical and food industries. Filters containing activated carbon are used in many modern models of devices for purifying drinking water to improve the organoleptic properties of water – the undesirable smell, taste, color, the content of chlorine, pesticides, organic compounds is also significantly reduced.