A stain is a mark or discoloration on a surface, often caused by the absorption of substances like food, drink, or dirt. Stains can occur on various materials, including fabric, wood, and walls. They can be temporary or permanent, depending on the type of stain and how quickly it is treated. Different types of stains require specific cleaning methods. For example, oil stains may need a degreaser, while ink stains often require alcohol-based solutions. Understanding the nature of the stain is essential for effective removal, as some stains can set over time, making them more difficult to clean.