Iron is an Allomantic metal that, when burned, allows the user to Pull on various metal objects around them, pulling any of these objects towards
them. The burning of Iron is affected by normal laws of physics, so when the user pulls upon something with more weight, it will take more iron to move this, and if the user pulls upon something with more weight than themselves, they will be pulled through the air towards the aforementioned object. The burning of Iron is used to fly, manipulate various objects, pull someone towards you (assuming that they have metal on their person), disarm somebody with a metal weapon, change the flight path of flying coins (see Copper Clip and Steel), and for a multitude of other things.
When used in Feruchemy, Iron allows one to store physical weight in a metal mind, allowing one to decrease their weight by storing it and temporarily increase their weight by withdrawing the stored weight. An interesting note is if someone were to master both Feruchemy and Allomancy, then they could increase their weight to pull any object towards them with Iron, push any object away from them using Steel, or decrease their weight to use Iron and/or Steel to move through the air towards or away from any metal object, no matter the weight.
When used in Hemalurgy, Iron is used to transfer the attribute of human strength.