VACUUM output

Hi, everybody!

I was wonderring if someone could please explain to me how to read the
output of a VACUUM command?
For example:

NOTICE: --Relation dnbarchive--
NOTICE: Index history_idx: Pages 682674; Tuples 147407062: Deleted 7034.
CPU 190.55s/164.38u sec elapsed 5913.35 sec.
NOTICE: Removed 7035 tuples in 110 pages.
CPU 0.02s/0.08u sec elapsed 2.29 sec.
NOTICE: Pages 1180651: Changed 46177, Empty 0; Tup 147339618: Vac 7035,
Keep 0, UnUsed 16938612.
Total CPU 549.83s/218.90u sec elapsed 13697.71 sec.

What is the meaning of these statistics? Partciularly, "Vac", "Removed"
and "UnUsed"?
In this case, do I interpret it correctly, that I have over 16 million
unused tuples, and only about 7K of those were taken care of by vacuum?
If so, what do I need to do to fix that?
Is increasing free space map going to help?
If so, will it make the vaccum run even longer? (I started it yesterday
about 6 pm, and it is still going - looks like not even half way
through)....

Thanks a lot!

Dima