Plate Mail is a type of medieval armor and a very common item of equipment in most Fantasy Role-Playing games. This is also the armor you see worn by knights most often in medieval movies.
Plate mail is made from heavy steel plates affixed to a backing of leather and chain mail. These plates are of a superior construction to those found in banded mail or in the older bronze plate mail. They use a lightweight steel with impressive protective qualities.
This armor is highly associated with French medieval culture, and many of the segments of the armor are referred to by their French names. The plastron-de-fer is the breastplate, which protects the vital organs from all manner of attack. Epaulieres, or shoulder guards, protect the shoulders from smashing attacks. Grevieres are plates that protect the lower legs, while gauntlets and a helmet are also considered part of the suit.
This is the most common type of heavy armor, the heavier field plate and full plate never became as common as the advent of firearms quickly rendered armor useless (which is why modern soldiers don't troll around the battlefield in armored suits). Plate mail is actually one of the more flexible armors, the complicated system of straps provide for a wide range of adjustment that no earlier armor had. The basic plate mail design was perfected more than any other type of medieval armor, with any improvements quickly adopted across the continent.
It may take several years income to purchase a suit of this armor, but it is worth every penny, anyone whose life it has saved can attest to that. This is the most common armor among veteran knights, adventurers and mercenaries, and will last for many years as long as it is properly maintained.