What does "first class" mean?

[Tom Loredo]

Hi folks-

I've often seen reference here (and on the Ruby page) to Python's
treatment of functions and methods as "first class objects."  What
does this mean?  I thought I had most of the OO lingo in hand after
a year of EE/CS courses at MIT in the early 80s (back then most it
fell under the rubric of "data abstraction").  But "first class"
in this context must have been in one of the lectures I missed.
(There were quite a few of those, actually!)

Thanks,
Tom Loredo