A stain, in the context of a mark, refers to a discoloration or blemish on a surface, often caused by the absorption of a substance. Stains can occur on various materials, including fabric, wood, and walls, and are typically the result of spills, dirt, or other contaminants. Removing a stain often requires specific cleaning methods or products, depending on the type of material and the nature of the stain. Common cleaning agents include detergents, bleach, and stain removers, which are designed to break down the substances causing the discoloration.