A kitchen utensil that is also called a potato ricer, and which is a kind of potato masher. It looks sort of like a giant garlic press, with a container (sometimes called a hopper) with many small holes in it. Into the hopper fits a plunger. The whole contraption has two handles, one with the plunger on it and the other with the hopper on it. You put cooked food such as potatoes, carrots, or turnips into the hopper, position the plunger on top of the food, and squeeze the handles together; out extrudes your food, mashed. I suppose if you squint your eyes the extruded food vaguely resembles rice. Culinary experts particularly recommend ricers for making mashed potatoes, and for good reason: armed with this, mine are the best they've ever been, smooth and creamy and soft.
I got turned on to the ricer some years ago on the recommendation of Joy of Cooking and Cook's Illustrated, my culinary gurus (at least in terms of the printed word). I went to a good cookware store, and was amazed at the variety of types of ricers available, especially considering I'd only recently even learned of their existence. The most common types, though, have round or V-shaped hoppers and are made of stainless steel or cast aluminum. Some have removable disks with different sized holes for finer or coarser mashing.
A word of warning: ricers work best with peeled vegetables, and are not particularly easy to clean. But in my humble opinion a little extra sweat in pursuit of gustatory pleasure is well worth it.