To disclose means to reveal or make known information that was previously hidden or secret. When a company discloses its financial results, it shares detailed numbers that show how much money it made or lost. When a scientist discloses her research findings, she publishes them so other scientists can review and build on her work.

The word often appears in formal or official contexts. Witnesses in court must disclose what they know about a case. When you apply to a school or job, you might need to disclose any conflicts of interest. A journalist might disclose her sources, or choose to protect them.

Disclosure is about sharing information that someone has a right to know or needs to know. If your friend asks whether you liked their drawing, being honest isn't really disclosure: it's just answering a question. But if you knew your friend had copied someone else's drawing and you revealed that fact to the teacher, that would be disclosing important information.

Notice that disclose sounds more formal than simple words like “tell” or “reveal.” You wouldn't say “I disclosed to my mom that I was hungry.” But you might hear that a company “disclosed a data breach” or that officials “disclosed the details of their investigation.” The word carries a sense of official responsibility and importance.