In a non disclosure agreement (NDA) you agree on the scope of the information you will not disclose.

NDA's play an important role in my professional life, sometimes I get the feeling It might be saver to stop talking at all. It's important to read them and make sure you fully understand the content. The strictest one I encountered is the one Blizzard asks their future employees to sign. If it would be followed to the letter you can't even tell your partner anything more than that you work somewhere.