A PDA is a "personal digital Assistant", a generic term for many handheld computers used to store data, run software, etc. See this site for tons of info and related links: http://en.wikipedia.org/wiki/Personal_digital_assistant
I've been using an HP hx4700 Pocket PC (now discontinued) since I started nursing school
. I used it to take notes in class (with a bluetooth keyboard) and as a replacement for a boatload of reference books. In addition to those uses, I am also able to use it to wirelessly access the 'net both at home and at work. For my purposes, it basically serves as a laptop computer replacement.
The most useful feature at work has been all the drug references that I've loaded. My favorite software site is www.skyscape.com
, but there are many others. I believe that anyone who is reasonably computer-literate (or is simply willing to learn) will be able to benefit from a PDA.