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.
Control-Up and Control-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.
Edit>More Selection>Select Paragraph (shortcut: Control-E P) selects the paragraph containing the caret.
Edit>Text>Format Paragraph (shortcut: Control-E F) splits and joins lines in the current paragraph to make it fit within the wrap column position. See Section , “Wrapping Long Lines” for information and word wrap and changing the wrap column.
Edit>Text>Delete Paragraph (shortcut: Control-E D) deletes the paragraph containing the caret.