[Newbie Q] Detecting what packages are defined

I've read the documentation -- even the Hyperspec, tho' it gives me a headache.  I must not have seen the "right" document, because I miss the answer to a simple question:

How can I determine what packages are already defined?

I see a lot of symbols that look like package-names in *FEATURES*, but nothing to suggest that that is automatic or even recommended.  If I look at *MODULES*, the names I see don't look like known packages; and of course *MODULES* is "depreciated."

The spec seems to require that the namespace of package-names is unique and separate from any other namespace, so enumerating it shouldn't be such a big deal.

TIA
-- 
In real life: David A. Cobb, semi-retired mainframe t-rex, trying to evolve.