A more thorough explanation:

Closed court refers to a historical English Court of Common Pleas that was only open to serjeants-at-law. This monopoly was abolished in 1845. It can also refer to a closed session in which parties not directly involved are not admitted, such as during a military court-martial when members deliberate alone.

For example, during a military court-martial, there is a closed court session where only the members or the judge deliberate alone. This ensures that the decision-making process is not influenced by external factors.