What is the term used for the clearance of meshing gears of any diametral pitch?

The term used for the clearance of meshing gears is known as backlash. Backlash refers to the slight gap that exists between the teeth of gears when they mesh together. This gap is intentional and is created to allow for smooth operation of the gears, especially during thermal expansion, lubrication, and to accommodate manufacturing tolerances.

Having the right amount of backlash is crucial in gear design as it prevents binding that could happen if the gears are too tightly meshed, which in turn can lead to increased wear and premature failure. It's also significant in maintaining precise control over the operation of machinery, particularly in applications requiring high accuracy.

Although other terms such as tolerance, dedendum, and addendum relate to gears, they refer to different aspects of gear design and function. Tolerance is about permissible limits on dimensions, while dedendum and addendum specifically refer to the depths of the gear tooth spaces below and above the pitch circle, respectively. None of these terms cover the intended concept of clearance in the meshing context that backlash does.