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The term peculiar galaxy indicates a galaxy that is not fully described by its overall galaxy classification (the Hubble sequence), i.e., that in addition to being spiral or elliptical, it 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. (If a galaxy simply doesn't fit the description of spiral, disk or elliptical, it is not termed peculiar, but irregular.) Classifying a galaxy as peculiar is based upon its appearance and requires some judgment and determinations do not always agree. 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.