A. Nafl Tawaf is the optional (voluntary) Tawaf that any sane person can perform during their stay in Makkah, without being bound by specific timings. It can be done once or multiple times, at any time.
In Nafl Tawaf, Ramal (walking briskly in the first three rounds) and Ittiba (placing the upper garment under the right arm and over the left shoulder) are not required, and there is no condition of wearing Ihram.
For an Afaqi (a traveler from outside the Meeqat), performing Nafl Tawaf is more virtuous than offering Nafl Salah (optional prayer).
However, for the residents of Makkah, offering Salah is considered more virtuous than performing Tawaf — but this ruling is specifically for the Hajj season, to avoid crowding and to make space for the Afaqis. Otherwise, Nafl Tawaf is considered better.