Define the term 'clearance void time' and its relevance.

Clearance void time is a specified time given by air traffic control (ATC) in a departure clearance, after which the clearance is automatically canceled if the aircraft has not yet begun takeoff. This term is used primarily at airports without an operating control tower or at part-time towered airports when the tower is closed. The purpose of a clearance void time is to ensure that an aircraft does not enter controlled airspace without ATC awareness and approval. When an aircraft receives a departure clearance with a void time, the pilot must begin takeoff before that specified time. If the aircraft is unable to begin takeoff before the void time, the clearance is no longer valid. The pilot must then contact ATC again to request a new clearance. For example, an aircraft departing a non-towered airport might receive a clearance that states, 'Cleared to the Anytown Airport via the Victor 123 airway, maintain 3,000, expect 5,000 ten minutes after departure, void time 1400 Zulu.' This means the pilot must begin the takeoff roll before 1400 Zulu time. If the takeoff is not commenced by 1400 Zulu, the clearance is void, and the pilot must contact ATC again to obtain a new clearance before departing. The relevance of a clearance void time is that it provides a safety mechanism to prevent unauthorized entry into controlled airspace. Without it, an aircraft could potentially depart and enter controlled airspace without ATC knowing its intentions or current status, which could lead to conflicts with other aircraft. Therefore, clearance void times are essential for maintaining order and safety, especially at airports with limited ATC services.