A confusing subject! Broccoletti are usually just a name for cima di rapa (the leaves, stems, and buds of a variety of turnip). But they can also be: young broccoli, or else broccolini (a hybrid, slender-stalked broccoli).
Around Italy you'll also hear cima di rapa called friarielli (Campania), rapini, rape, rappi or broccoli di rape.
Images by: cigno5