executive privilege as in: when claimed by US President
The Supreme Court found that, once executive privilege is invoked, a presumption of privilege is established.
the right of the U.S. President and the executive branch to withhold information from other branches of government (typically Congress) if it might interfere with the executive branch’s ability to govern
The U.S. Supreme Court ruled that executive privilege is necessary to enforce separation of powers, even though it is not explicitly mentioned in the constitution. Typically the President wants to keep military or diplomatic secrets, or wants to preserve a climate where others can offer opinions without worrying that anything they say may be made public in the future.
Once claimed, there is a presumption of privilege, but a court can deny it. Almost every president has claimed executive privilege when denying a Congressional request for information, but such claims seldom go to court. Typically the executive branch claims privilege and then offers compromise information which Congress usually accepts.