PFD is an acronym for Personal Floatation Device... defined as: a device designed to keep one (1) person (thus, personal) afloat in water.
http://www.google.com/search?hl=en&rlz...on&ct=title
This includes (but is not limited to) life jackets, life vests, flotation cushions and rings.. etc
A life jacket is a PFD, but not all PFD's are life jackets!!!