Defunct processes

Ok...we have 3 production servers--Alpha ES40 running Tru64 5.1 Patch Kit 3. We have noticed a ton of defunct processes running on the server that is the "online" server. These processes don't appear in near the same numbers on the backup servers--but if we bring a backup server online, the defunct processes start appearing. I was curious last night and ran the following: ps -A |grep defunct | wc -l and there were right around 10400 defunct processes. Now I have no idea what a defunct process is. Also I'm not sure how bad they are, because they've been there for a long time (months and months and months) but just today the big-boss-man decided that they need to be looked into. So my very general questions are: what are these processes, are they normal or is there something wrong with our production application (big surprise there), and what do we do about them? The only things these systems are running is: TU 5.1, Informix (IDS 2000, client SDK, and SQL), Passport, and Xipc. I know it's a very general question...but I just need to know where to start investigating.