Many people treat the ideas of attorney-client privilege and confidentiality as identical.  While they are similar, they are not exactly the same thing.  There are at least two major differences between privilege and confidentiality.

First, there is the nature of these two ideas.  Confidentiality is a duty that is placed upon an attorney.  It is an affirmative requirement that compels an attorney to act in a certain way.  Specifically, it is a duty that the attorney has to avoid giving out any information about a client.  By contrast, privilege is an exemption from a duty.  In general, people have a duty to testify when they are compelled to do so by a government entity.  The attorney-client privilege exempts the lawyer from having to do so.  This means that confidentiality is a duty while privilege is an exemption from a duty.

Second, there is the scope that each idea covers.  Confidentiality applies to practically everything about the interactions between a client and an attorney.  By contrast, privilege only applies to some very specific interactions.  Privilege only applies to any communications between the attorney and the client that is given for the purpose of getting legal representation. 

Thus, these two ideas are similar, but they are not the same thing.