I also don't see the problem with calling a group of lines intended
to be re-flowed a "paragraph".
"Paragraph" seems like a nice intuitive term to me. In TeX, for
example, a "paragraph" is the one and only construct that flows (has
line breaks inserted automatically). Keith hinted that "paragraph"
too loaded a term; maybe he'd like to explain that in more detail.
The word "paragraph" describes the semantics of the block of text; it
implies, for instance, that the block of text contains one or more
sentences (some say two or more) on a single topic that are spoken by
a single speaker. For instance, it would not be appropriate for a
text-to-whatever translator to map a f=f "paragraph" into a "paragraph"
in some semantic markup language.
But if "paragraph" is the closest term you can find, use it, and just
point out that it's not quite the same as a "real" paragraph.