Mulch is any material spread over soil to act as a protective cover. It saves water by protecting soil from sun and wind, improves plant growth by stabilizing soil temperature, and reduces weeds by preventing light from reaching seeds. There are two main types - organic mulches from plant materials that break down over time improving soil, and inorganic mulches like rock that require less maintenance. Applying a 2-5cm layer of mulch around plants, being careful not to bury stems, helps retain water and suppress weeds.