Confidential information is any information that is not known to the public, and which must not be disclosed without permission.
This information can be any type of information such as personal information, business strategy information, and particularly information relating to inventions and designs.
Before filing a patent application it is essential that the invention is kept confidential as public knowledge will render the application devoid of novelty. However, sometimes in order to evaluate the invention, or build a prototype for example, it is necessary to disclose the invention to a third party. If this is done under an understanding of confidence, and preferably a confidentiality agreement, then the invention or aspect of the invention has not been disclosed to the public and the invention may still considered novel. If the third party then discloses the information, they can be sued, provided of course that the information is still otherwise confidential.
When using the services of any professional there is an automatic understanding of confidence.