Dimensional tolerances refer to the permissible limits of variation in a physical dimension of a part or assembly. They ensure that components fit together correctly and function as intended, even when there are slight differences in size or shape during manufacturing. Tolerances are crucial in industries like automotive and aerospace, where precision is vital for safety and performance. These tolerances are specified using a system of measurements, often expressed in terms of upper and lower limits. For example, a dimension might be stated as 10 mm ± 0.1 mm, meaning the actual size can range from 9.9 mm to 10.1 mm. Properly defined tolerances help reduce waste and improve quality in production processes.