Lead

Leads are utility items used to leash and lead certain entities. Leashed entities can be tied to fences or other entities by using the fence or entity while sneaking. A lead can be removed from an entity by shearing it.

Wandering traders always spawn with 2 trader llamas, each held with a lead. When a trader llama is detached, either by killing it or the wandering trader, dragging them far apart, using shears, or putting the llama in a boat or a minecart, the lead drops at the llama's position.

Using a lead on a mob ties the lead to the mob, allowing it to be moved by the player. Multiple mobs can be held by leads at once, but each mob held requires its own lead. Mobs can also be attached to other mobs with leads.