Lead

Leashes are items used to hitch animals to fence posts or nether brick fence posts, and also to lead them around.

Crafting
As of 13w16a, there is no crafting recipe for the leash.

Usage
Right-clicking with a leash in your hand will tie it on the animal that you are facing.

Most passive mobs can be "leashed". These include pigs, chickens, cows, mooshrooms, horses, sheep, squids, Iron Golems, Snow Golems, and wolves. The Bat is the only passive mob which cannot be leashed. Note that leashed mobs that naturally despawn (like squids) still despawn. If leashed animals are ten or more blocks away from the player leashing them, the leash will "snap" and turn into the item.

Trivia

 * The leash can extend out to 5 blocks when tied between a fence post and a mob.
 * Untamed ocelots can be captured and tied up using a leash.
 * If you are in creative mode you can leash a mob and pull it into the air, or tie it to a high up fence post (see picture below).
 * Multiple mobs can be tied to the same fence post.
 * You can use the leash to capture several mobs at the same time and walk them around altogether.
 * There is no known way of crafting them as of yet.

Gallery
Leine Laisse 首綱 Поводок 拴绳