A more thorough explanation:

Definition: Noctem de firma (nok-təm dee fər-mə), n. [Law Latin “night of duty (payable)”] is a historical term that refers to the duty or custom of providing entertainment or provisions for a night. During the Norman Conquest, it was the duty or custom of entertaining the king for one night. It is also known as noctes or firma noctis.

Example: In medieval times, the lord of the manor had to provide noctem de firma to the king when he visited the manor. This meant that the lord had to provide food, drink, and entertainment for the king and his retinue for one night.

Explanation: The example illustrates how noctem de firma was a duty or custom that required the provision of entertainment or provisions for a night. In this case, the lord of the manor had to provide food, drink, and entertainment for the king and his retinue for one night. This was a way of showing loyalty to the king and maintaining good relations with the monarch.