A linear ruler, also known as a straight edge, is a tool used for measuring and drawing straight lines. It typically consists of a long, narrow strip of material, such as wood, plastic, or metal, with markings or measurements along its length. Linear rulers are commonly used in mathematics, engineering, and art, and come in various lengths and units of measurement, such as inches, centimeters, or millimeters. They are essential for precise and accurate measurements, making them a fundamental tool in many fields.