(1) Description of the pattern
This pattern means that important information is kept secret from citizens. This is useful when hiding corruption, nepotism, money laundering, smuggling, vote buying, tax evasion, etc. When information is kept private there is less chance that malfeasance can be noticed. With Opacity in place, over the years elite business and governments can distance themselves further and further away from any controls on them.
(2) Why the pattern is good (i.e. bad)
This pattern is good because it prevents people from seeing how business and governments actually conduct their affairs. This encourages corruption because there is no oversight.
It can also establish this as a habit which ultimately can be seen as the "natural state of affairs", the way things are actually supposed to be.
(3) How it works
Keeping things from the public eye can be maintained through laws or habit. Sometimes when there are transparency laws, a government can designate things to be secret in order to maintain state security.
Links (to other anti-patterns)
This pattern is strongly linked to corruption patterns. It's really the handmaiden to corruption.
This pattern also could link to toothless journalism and to laws against activist or muckraking journalism. With the right type of laws, it would be easy to jail journalists for "slander" if they suggest that there might be malfeasance behind the closed doors — even if it happens to be true!