What is a direct drive fan? What is a conventional (or gearbox-driven) motor? And what is the difference?

A direct drive fan is a smaller, quieter, more efficient motor compared to a gearbox-driven motor. With a gearbox-driven fan, the motor provides powers the gearbox, which in turn powers the blades to turn. A direct drive uses a motor to power the blades, eliminating the need and issues related to a gearbox.