The term peculiar galaxy indicates a galaxy that is out of the ordinary and not fully described by the overall galaxy classification (the Hubble sequence), i.e., that has morphological peculiarities. The code p or pec is sometimes used as a suffix or final word in the classification to indicate such a galaxy. Classifying a galaxy as peculiar is based upon its appearance and requires some judgment and there is not consistent agreement. Peculiarities include tidal tails and unusual bars and/or spiral arms, and generally are attributed to galaxy mergers or tidal interaction. The visible peculiarity may result from the galaxy being active, but many active galaxies have no such visible peculiarity and are not classified as peculiar.