Students of the US Congress generally say that there are either 3 or 4 kinds of committees in Congress.
The most important and most common of these is called the "Standing Committee." These are committees (in both the Senate and the House) that are permanent and which have permanent jurisdictions and duties. These are the committees like Defense and Judiciary. These committees have subcommittees as well.
The second kind of committee is a select or special committee. This kind of committee is set up on a temporary basis for some particular task.
Third, there are joint committees. These are permanent, but are made up of members of both houses. They are generally not charged with legislative duties -- they are more just for administrative stuff like overseeing the Government Printing Office.
Finally, there are conference committees. These are a special kind of joint committee. They are appointed on a temporary basis whenever the two houses pass different versions of the same law. When this happens, the conference committee has to iron out the differences and produce one identical version of the bill.