"Definitive" means that whatever your talking about is the last word
on its subject matter
. Its usual context
is "the definitive work", which means a book
that is forever after
and source material
for any other publications or research
on that subject. To write the definitive work on a subject, you either need to be an incredible expert
or to be the first
to study it, but ideally both.
Everything2 is the definitive reference for everything Or it will be, someday.