Confidentiality / Non-disclosure Agreements
A Non-Disclosure Agreement (sometimes called a confidentiality agreement) is used by an inventor to reveal an unpatented idea to a party. The inventor has the other party sign a document that says they will not disclose any of the information to anyone else, and will not compete with the inventor.
I strongly discourage revealing your invention until you have filed a patent application even if you have a Non-Disclosure Agreement. Non-Disclosure Agreements should be used sparingly and only when disclosure of your idea to another party is required.
It is far better to discuss your invention in general terms and not reveal how it works prior to the filing of a patent, than to reveal important details and rely solely on a Non-Disclosure Agreement.
Remember that to enforce a Non-Disclosure Agreement, you may have to go to court. Even if you eventually win, the litigation will cost alot of time and money that should be going towards developing and marketing your product. Additionally, keep in mind that a Confidentiality / Non-disclosure Agreement is typically only enforceable against a party to the contactual agreement. This means that you will not be protected if the invention is stolen by someone who has not signed the agreement.