A more thorough explanation:

Term: de non decimando
Definition: De non decimando is a legal term that means a claim for exemption from paying tithes. Tithes are a portion of one's income or produce that is given to the church. This claim can be made by showing that the land was previously exempt from tithes or by proving that the land was once owned by the king or the clergy. However, this claim only applies to the person making the claim and not to their tenants or lessees. For example, if a farmer can prove that their land was previously exempt from tithes, they can make a claim for de non decimando and be exempt from paying tithes. However, if they rent out their land to another farmer, that farmer would still be required to pay tithes.