There's a lot to tell about Plone.

"Plone is a ready-to-run [[content management system]]
that is built on the powerful and free [[Zope]] [[application server]]."  So says the 
"[[http://plone.org/about/plone/|What is Plone?]]" page of the 
[[http://plone.org|Plone Web site]].  Wikipedia also 
[[http://en.wikipedia.org/wiki/Plone_(content_management_system)|has plenty to say]]. 

[Explain what this means.]

Plone.org maintains Wikis, but apparently only to process
fault Tickets, that is, as a 
"[[http://dev.plone.org/plone/wiki/|bug and feature tracker]]".
There's nothing directly comparable to the Python Wiki.

A PloneSprint is frequently scheduled--half-a-dozen times annually?
There are local user group meetings, annual conferences, ...

Plone is particularly prominent in Latin America, Europe, ...

Plone progress is managed in terms of 
[[http://plone.org/documentation/glossary/plip|PLIP]]s
and [[http://plone.org/products/plone/roadmap|roadmap]]s.