The exchange below points out a possible confusion of terms (which I often
see, and sometimes commit): the term "webpart" is used to mean "a .dwp or
.webpart file that can be installed and used to create a display in a web
part zone on a web part page" -- informally, at least, it could be
considered a "class"; it's also used for an instance of that class, as
instantiated to be run in a particular web part zone on a particular web
part page.
What's even more confusing, the term "web part" is often used when what is
really meant is the list or library on which the web part provides a view.
I suspect that this last is the meaning intended in both the question and
the reply below, but it took me a while to come to that notion.
Perhaps Microsoft made this last confusion worse in their "Add a Web Part"
interface; there is a "class" for each list and library in the site, as
well as the more general classes. So the name "Shared Documents" is a
library name, but it is also a web part class name (at least in the UI), on
a par with "Content Editor Web Part". If they had chosen instead to have a
"Library View" web part, in which the specific library was a parameter to
set, this confusion could have been largely avoided.
This is just a heads-up; I am far from believing that there's any way to
control how people use terminology. But those who care might make an extra
effort to distinguish these different meanings in use.