In medieval times, there were dozens of different kinds of armor that were worn by soldiers, knights, and mercenaries. With each improvement in armor quality, there was a bit of a tradeoff for maneuverability.
However, a trained soldier could learn to maneuver while wearing heavy armor, making them some of the deadliest foes on the battlefield.
Medieval armor starts at leather and moves up to full plate.
Leather armor, the most common armor, was made of hardened pieces of leather, and could protect against slashing weapons in close combat but not much else.
The next step up, studded leather, had metal studs covering the leather, which provided added protection but not a lot. From studded leather armor moved to ringmail and chainmail. This armor was made up of several hundred links of chain or rings, and provided the protection of metal with better movement than full plate.
Plate armor is what most knights wore, and is as its name implies, is comprised of hardened plates of metal. This armor provides maximum protection, and sometimes, knights would also wear a chainmail hauberk underneath plate armor which would make them near indestructible. In fact, to defeat a knight in full plate armor, one would often have to tire them out or find a way to strip their armor.