Shallots and onions are both members of the allium family but have distinct characteristics. Shallots are smaller in size, with a slightly elongated shape and multiple cloves within a single bulb. They have a sweeter taste with a hint of garlic. On the other hand, onions come in various sizes, shapes, and colors, and they possess a stronger and more pungent flavor. Shallots are often favored for their subtlety and ability to provide a more delicate onion flavor to dishes.