My cousin literally just made a post about this on Facebook.com. I will update this for you after I get my facts straight.
According to Google.com.
an organization whose members are sworn to secrecy about its activities.
That is a very broad definition. This basically tells your, that their are many different types.
For example, I once worked for a cable company, and by law, I had to sign a paper stating that I will not reveal the technologies and secrets that are given to me. To this day, I dare not speak if those things, because who knows what rule I would still be breaking.
