Usually this is called a "leave of absence" in which the employer grants unpaid time off, but the position is still reserved for the employee when they return.

Usually this is called a "leave of absence" in which the employer grants unpaid time off, but the position is still reserved for the employee when they return. I have only seen a few employees request these in the past, though employers are probably open to other terms if they are willing to entertain this type of request in the first place