Short answers, pulled from the story.
A shield is a piece of personal armour held in the hand, sometimes strapped to the wrist or forearm, used to intercept close-range weapons like spears and ranged projectiles like arrows. Ancient armies from the Mycenaean Greeks to the Roman legions relied on shields both for individual protection and for forming defensive formations such as the Greek phalanx and the Roman testudo.
The oldest surviving shields date to the Bronze Age. Examples such as the Yetholm-type shields from the Bronze Age and the Iron Age Battersea shield are among the best known, though these are generally considered ceremonial rather than practical battlefield weapons.
The kite shield, introduced by the Normans around the 10th century, was rounded at the top and tapered at the bottom, offering protection for a horseman's legs. The heater shield replaced it by the 14th century as body armour improved; it was smaller, made of laminated wood layers, and its shape became the basis for the symbolic heraldic shield still used today.
A buckler is a small round shield typically between 8 and 16 inches, or 20 to 40 centimeters, in diameter. Unlike most shields, which were made of wood, the buckler was usually made of metal. It offered little protection from missiles but was designed for hand-to-hand combat, where it served both defensively and offensively. Its use extended from the Middle Ages into the 16th century.
Zulu warriors carried a shield called the Ishlangu, made from a single ox hide supported by a wooden spine. These shields were especially long and broad, often covering much of the body, and were used in combination with a short spear called the iklwa and sometimes a club. Zulu warriors continued using war shields into the 19th century.
Modern law enforcement uses two main types: riot shields, made from metal or transparent polymers such as polycarbonate Lexan or Makrolon, designed to protect against rocks, bottles, and blows from crowds; and ballistic tactical shields made from materials such as Kevlar, rated at Level IIIA to stop pistol cartridges or Level III and IV to stop rifle cartridges. Tactical shields often include a firing port and a bulletproof glass viewing window, and are deployed by units such as SWAT teams.