Grout is a thick paste used to fill the spaces between tiles, providing stability and preventing moisture from getting underneath. It is typically made from a mixture of water, cement, and sand, and comes in various colors to match or contrast with the tiles. Once applied, grout hardens and helps to create a seamless look in areas like bathrooms and kitchens. Regular maintenance, such as cleaning and sealing, is important to keep grout looking fresh and to prevent mold growth, especially in damp environments like bathrooms and kitchens.