A more thorough explanation:

Definition: Knight's service is a type of land tenure where a knight holds land from another person or the Crown in exchange for a promise to provide military service.

For example, a knight might hold land from the king and promise to provide military service for forty days each year. This was known as the "service of one knight" or "servitium unius militis."

This type of tenure was common in medieval England, where many knights held land from the king in exchange for their military service.

Overall, knight's service was a way for knights to gain land and status in society, while also fulfilling their duty to provide military service to their lord or the Crown.