Lay open is a phrase that means to REVEAL or EXPOSE something. It can also mean to UNCOVER something. This phrase is often used when referring to a situation or an object that has been hidden or kept secret. For example, if someone were to lay open a secret document, they would be revealing the contents of the document to the public. Similarly, if someone were to lay open a hidden room, they would be uncovering the room and making it accessible to others.