Giant Question Block
From the Super Mario Wiki
Giant Question Blocks (or Giant ? Blocks) are blocks found in Super Mario Bros. 3 and its remakes. They are found mainly in the game's World 4 (Giant Land), but can also be found in certain secret areas throughout the game. They contain regular power-ups in Giant Land, and usually multiple 1-Up Mushrooms or various Suits - such as the Tanooki, Frog, and Hammer Suits - in bonus areas.