Barzel means literally iron. It is one of the 5 PRINCIPLES of the JDL.
I Ahavat Yisroel – Love of Jewry
II Hadar – Dignity and Pride
III Barzel – Iron
IV Mishmaat – Discipline and Unity
V Bitachon – Faith in the Indestructability of the Jewish People.
The translation is Iron Dome.
Todah, Mesta! :)