Question: how is elrond half elven?
Answer: The Half-elven, or Peredhil, were people of Middle-earth, the name of whom was primarily applied to Elrond and Elros in the Second and Third Age, but also to Eärendil and his wife Elwing before them. They were called so because of their mixed Edain (Human) and Eldarin (Elven) blood.