an amorphous, highly adsorbent form of silica used as a drying agent in air-conditioning equipment, as a carrier of catalysts in chemical reactions, etc.
See silica gel in American Heritage Dictionary 4
noun
Amorphous silica that resembles white sand and is used as a drying and dehumidifying agent, as a catalyst and catalyst carrier, as an anticaking agent in cosmetics, and in chromatography.