Ferrous in non-chemical contexts is a general adjective for iron. For
example, referring to "ferrous metallurgy" includes the production
of metallic iron, including wrought iron (commercially pure iron, with less
than 0.2% carbon), cast iron (with 3.5-5% carbon), steel (with a carbon
content between them), or other alloying elements.
Iron is believed to be the tenth most abundant element in the universe, and
the fourth most abundant in the Earth's crust. The concentration of iron in
the various layers in the structure of the Earth ranges from high (probably
greater than 80%, perhaps even a nearly pure iron crystal) at the inner
core, to only 5% in the outer crust. Iron is second in abundance to
aluminium among the metals and fourth in abundance in the crust. Iron is the
most abundant element by mass of our entire planet, making up 35% of the
mass of the Earth as a whole.
Ferric is a term that means containing or having to do with iron, derived
from the Latin word ferrum, meaning "iron". In chemistry the term
is reserved for iron with an oxidation number of +3, denoted iron(III) or
Fe3+, whereas ferrous indicates that it has oxidation number of +2, denoted
iron(II) or Fe2+, which combine with other atoms to form molecules.