NDAs are pretty common in freelance work projects. The acronym NDA stands for "Non Disclosure Agreement", which basically means that you are not allowed to talk about anything related to clients, vendors, hardware or software specifications, market strategics, etc.
While I understand (and of course respect) the origins and purposes of NDAs, sometimes they're troublesome anyway. For instance, I am working on a really really cool project that is eventually going to be Open Source and have an important impact there, because... I would love to tell you more, but I'm not allowed to :)
This is a difference between academics and businesses I will have to live with.