What is the difference between a concealed hand and an open hand?

A concealed hand is one where all sets were drawn from the wall without claiming any discards; every meld is hidden until the win is declared. An open hand has at least one meld claimed from another player's discard, which must be laid face-up on the table immediately. Concealed hands are generally harder to build but unlock higher-value scoring combinations, while open hands are more flexible but limit access to certain fan bonuses.