What is the intention for fasting on Mondays and Thursdays, and is it a Sunnah, a Nafl, or a voluntary act, and what is the reward for fasting them?

"Sunnah," "Nafl," "Tatavvu'," and "Nadab" are synonymous terms. The reward for fasting is known only to Allah, as He says: "Every deed of the son of Adam is for him, except fasting; it is for Me, and I shall reward for it." The reason for choosing to fast on Mondays and Thursdays is that deeds are presented to Allah on these days, and one loves for their deeds to be presented while they are fasting.