Paint thinner is a solvent used to dissolve or thin oil-based paints and varnishes. It helps in cleaning brushes and tools after painting, making it easier to remove dried paint. Common types of paint thinner include mineral spirits and turpentine, each with specific properties and uses. When using paint thinner, it's important to work in a well-ventilated area due to its strong fumes. Safety precautions, such as wearing gloves and a mask, are recommended to avoid skin irritation and respiratory issues. Proper disposal of paint thinner is also essential to prevent environmental contamination.