Incomplete is a deck-status tag indicating that a decklist is still being built, revised, or filled out. It has no rules meaning and can apply to anything from a rough pile of ideas to a nearly finished deck missing only a handful of cards.
An incomplete Commander list might still need its final mana base, interaction package, or last ten cards, while a Constructed deck could be awaiting a sideboard. The tag simply warns viewers that the current list isn't intended as a finished product.
