This term means to manifest rectitude or upright conduct. The term was originally used to describe qualities expected of the sovereign. De (德) specifically meant fairness and decency towards the populace, in the appointment of officials, and the bestowing of rewards and punishments. Mingde (明德) as a verb was to govern in such a way. Later, the term as a noun referred to the required moral qualities of those in power. Confucianism holds that governing in a moral way is an extension of a person’s internal rectitude, hence mingde is an expression of the highest degree of morality manifested by a ruler.
Your illustrious father King Wen of Zhou displayed virtue to his people. He punished sparingly, did not disrespect the bereaved, appointed those with ability, recognized those with good qualities, and intimidated those who needed to be deterred. (The Book of History)
The way of great learning is to illustrate high morals and proper conduct, show compassion to the people, and follow the principles of benevolence and virtue.(The Book of Rites)