As far as jEdit is concerned, “paragraphs” are delimited by double newlines. This is also how TeX defines a paragraph. Note that jEdit doesn't parse HTML files for “<P>” tags, nor does it support paragraphs delimited only by a leading indent.
C+UP and C+DOWN move the caret
        to the previous and next paragraph, respectively. Holding down
        Shift in addition to the above extends the selection a
        paragraph at a time.
>>
        (shortcut: C+e p) selects the paragraph containing the
        caret.
>> (shortcut: C+e f) splits and
        joins lines in the current selection to make it fit within the wrap
        column position. If nothing is selected, the paragraph containing the
        caret is formatted instead. See the section called “Wrapping Long Lines” for
        information about word wrap and changing the wrap column.
>> (shortcut: C+e d) deletes the
        paragraph containing the caret.