Surds are a special type of mathematical expression that involves roots, typically square roots, that cannot be simplified into a rational number. In simpler terms, a surd is an irrational number that is left in root form because its exact value cannot be written as a simple fraction or a terminating or repeating decimal. Surds are important in mathematics because they represent exact values that cannot be simplified into neat fractions or decimals. They are often encountered in geometry, algebra, and trigonometry, especially when dealing with right-angled triangles, circles, and irrational numbers. Understanding surds allows you to work with these exact values without resorting to approximations, which is crucial for precise calculations in advanced mathematics.