The One Piece's "Episode of Nami" is not an anime episode because of its length. What is that episode categorized as?
Episode of Nami: Tears of a Navigator and the Bonds of Friends is a TV Special of the One Piece anime. It aired after Episode 560.
(From the One Piece wiki Episode of Nami)
It is the 5th TV special to be aired. The list of TV specials so far: