A dolly is a cart with two wheels and long handles used for moving heavy objects. Instead of carrying one box at a time, stack them on a dolly and wheel them all to the van at once.
A dolly, which you can also call a "hand truck" or a "two-wheeler," is an L-shaped device with a flat base that slides easily underneath a box or piece of furniture. Tilt the dolly back on its wheels, and it's fairly simple to transport things, even if they're too heavy for you to lift. Another meaning of dolly is "doll," as in a child's toy that looks like a little person: "Give your brother back his dolly!"