PCV stands for Positive Crankcase Ventilation. You can find a full description of the system here:
http://www.hastingsfilter.com/engine...tsb_94-2r.html
The PCV valve should be replaced regularly. It's inexpensive, but difficult to get to. Here's a diagram showing how the PCV valve attaches to the manifold. It's item number 2 on the diagram.
http://tinyurl.com/tncj