If you make a disclosure, you reveal information not previously known — either because it's new information or because it's been kept secret. Disclosure of new evidence at a trial could reveal that the accused is innocent of the crime.
The noun disclosure derives from the Old French word desclos, meaning "open, exposed, plain, explicit." If you make a disclosure, you put something out in the open, usually information that was formally secret. After the disclosure of your huge credit card debt, your parents might make you get a job. The disclosure that nicotine is really addictive has motivated many people to quit smoking. The disclosure of one coworker's salary to another could lead to bitter jealousy.