A training lead, also known as a long line, is a normal lead but longer. Usually made of a wide flat material so it doesn’t tangle. Usually without a handle as the idea is to let it trail behind the dog on the ground. You step on it if it looks like they are about to leg it, or if for any safety reason you want to bring them back to you quicker than they will recall. Long lines should be attached to a harness not a collar.
So not the same as retractable / extending lines.