Is it possible to find all documents in the index that do not contain a certain term? In other words, is it possible to make a query such as 'NOT <term>'?

Otis Gospodnetic

No, it is not possible to do that with Lucene. Lucene could be modified to do that, but such queries would be very slow.
c.f. http://marc.theaimsgroup.com/?t=100455365600001&r=1&w=2