What is a cold iron?

An iron might be anything, depending on context, as long as it is made of iron. A golfer uses a club that is called an iron, to distinguish it from the club called a wood. A housewife removes wrinkles from clothing with an iron. A horse drawn wagon carries a weight with rein attached so the driver can drop it on the ground for a temporary tether, and that weight is called "the iron". An tire repair shop has a tool called a tire iron used to separate the rubber from the rim.

So the answer just depends on what iron you are talking about.