What is the purpose of taxi fuel in aviation?

Taxi fuel is specifically designated for the activities of starting up the aircraft and taxiing to the end of the runway before takeoff. This fuel allowance ensures that there is enough fuel on board to cover the operational demands of getting the aircraft ready for departure, including engine start, taxiing on the ground to the active runway, and any potential delays during this process.

Being aware of the specific fuel requirements for these operations is crucial for effective mass and balance calculations; it helps pilots ensure they have allocated adequate resources for all phases of flight. The other options refer to fuel requirements that are necessary for phases of flight other than taxi, such as cruising at altitude, holding patterns, or takeoff and landing, but they do not pertain directly to the taxiing phase, thereby clarifying why those are not applicable in this context.