In some treatments, Cold Iron is iron that has never been worked with fire; this means that it has either been magically extracted or that it's meteoric iron. A few take it to mean Iron that's poured - IE, cast iron. (Cast iron as a weapon is generally poor.)

In traditional folklore, it's just iron, or iron that isn't still hot from the forge. 

Note that iron weapons (as opposed to steel) are more brittle.

In most systems, it excludes steel - not in the Dresden Files setting, as is evidenced in Storm Knight (with the pixies), as the common box cutter blade is usually cheap steel.

What is Cold Iron actually?
From Season 4, House has three new doctors as part of his team and the previous three just appear off an on. Why didn't the show's creators update the intro to show the new team? It always shows Cameron, Chase and Foreman.
