Shion with his shield, art by M DJ Boyann.
Shields are larges plates of metal or wood that can protect the holder from bladed, blunt and projectile weapons. Since they are held in one hand, they limit the warrior to just one weapon in their other hand, although this is often enough. With enough skill, the shield itself can be used as a battering weapon to stun or bludgeon the foe. Shion of the Wonder Boy series uses a shield adorned with a star that comes to good use when he loses his sword in Wonder Boy in Ghost World.
Shields can also come in other fashions. Large energy shields (or forcefields) can be created to bar entry to unwanted visitors, such as the one that surrounds the Floating Island at full power, or the sensor shield on Captain Plunder's ship that blocks him from the view of Captain Tiberius. Certain Badniks carry a kind of shield; Crawl uses its bumper as a literal shield, while Orbinaut cannot easily be destroyed if it continues to rotate spikes around itself. In the video games, Sonic the Hedgehog can find a wide variety of shields in TVs, some of which grant him extra abilities such as pulling in Power Rings, turning into a fireball or letting him breathe underwater. This has found its way into the comics, with Sonic able to conjure up an "Insta-Shield" by vibrating molecules in front of himself. Ebony can do something similar, instead using magic.
Blaze the Cat is a somewhat unique individual in that she is able to destroy certain shields with her powers. She initially displayed this talent by bypassing Ebony's personal forcefield (in "Order & Chaos"). Soon after, she was informed that she was able to pass through barriers of Chaos energy because the same power ran through her veins. This ability helped her and three Drakons break into a heavily-shielded House of Magic.
"Human" shields consist of somebody pulling someone else in front of them to take attacks, like when Commander Brutus used Amy Rose as one to fend off Super Sonic, not knowing he would attack anyone he feels like.