Unfilling a region joins all the lines in a paragraph into a single line for each paragraphs in that region. It is the contrary of fill-region, and the idea is based on UnfillParagraph.

(defun unfill-region (beg end)
  "Unfill the region, joining text paragraphs into a single
    logical line.  This is useful, e.g., for use with
  (interactive "*r")
  (let ((fill-column (point-max)))
    (fill-region beg end)))

;; Handy key definition
(define-key global-map "\C-\M-Q" 'unfill-region)