1. A person who is a realist and not an idealist. He/she sees the world for what it truly is and learns from its mistakes and in turn, becomes very successful in life.
2. One who has a vast knowledge about a certain subject, but is not obsessed with it. Don't get us confused with geeks as they are wanna-be nerds who have no life and are obsessed with whatever their fascinations are (usually WoW and shit).
It's unfortunate that there aren't more nerds in the world today.