Steel is a very hard substance usually made of metal. You have to have level 5 defence to wear steel armour. Which means it's not very good - it's not even as good as Black. Is Black even a real metal? I doubt it. And they stole mithril from LOTR as well!
Jeez. Sometimes Runescape is so confusing.
Now, let me get back to pwning that goblin.
Ha! I hit a 2 with my steel sword!
We are both winners today.