It doesn't stand for anything - AFAIK. It's the designation placed on the bottom of your boarding pass when CAPPS thinks you are potentially dangerous. CAPPS, of course, does stand for something - Computer Assisted Pre-Passenger Screening.

60 minutes did a story on numerous people who have been lumped into the DANGER group b/c of mistaken identities or similar names or something. This is leading to CAPPS II where you will be providing DOB when you make your reservation.

Frustrated by the invasion of privacy complaints, there is rumor (maybe fact) that there will be an opt-in trial this summer that lets you avoid potential delays by "pre-qualifying" if you choose to do so. Identification to include finger scan or iris scan has been discussed. I'm sure my understanding is slightly offbase, but it seems unfair nonetheless. Think about this, those that don't opt-in are more likely to receive further scrutiny.