inner geek: Geekish tendencies that reside within one's greater personality.
This term is frequently used to describe an action that may be considered geeky, such as playing Dungeons & Dragons. You are "indulging your inner geek." You may not memorize THAC0 tables or own every Dragonlance book, but you do get together with your friends every Thursday to kill some orcs. Or maybe you own a hefty pack of Magic cards, but you don't collect variant art printings of Serra Angels. Maybe you own Star Wars action figures. Whatever it is you do, that little bit of geekiness that resides within you, but doesn't dominate your personality, is your inner geek.
This term has arisen in the last ten years or so as many forms of entertainment that were considered geeky in the 70s and 80s, such as video games, are now becoming popular within pop culture. Video games are geeky, but not all who play them are geeks. "Inner Geek" plays upon the term inner child, which one was expected to occasionally indulge as they grew older.