The End is an dimension outside the one where Elementia exists. It is a dark void, filled with floating islands. Ender Magic is linked to this realm. Due to it's status as a shadow world, it is easier when travelling to/ from it to bypass Elementia's dimensional shield. It is ruled by the Ender Dragon
The First Ender Wizard was thought to have come from The End, as well as the Ender Scroll. He built Strongholds as links to The End, but none are known to still be active. Dragon was found in one, and has travelled to The End.