Masters are a type of hand shaped enemies in the Zelda series. They are one of the oldest family of enemies found in the series, debuting as soon as The Legend of Zelda. They have since made appearances in most Zelda games since.
Wallmasters are a type of Master that is usually found floating above Link may it be out of sight or in sight depending on the game. They will try to slam into Link from above and grab him. If they manage to grab Link, they will transport him back to the entrance of the dungeon or the room depending on the game. They may or may not be able to be defeated depending on the game. Their appearance also greatly carry from game to game. They can be regular hand, disembodied mummy hands, ghostly hands or artificial hands.
Floormasters are a type of Master that is usually found on the ground in opposite to the Wallmasters. They usually engage Link directly and will either try to harm him or grab him to send him back to the entrance of the room or dungeon depending on the game. Unlike the wallmasters, they debuted in The Legend of Zelda: Ocarina of Time. They usually either appear to be connected to the ground with an arm or levitate above the ground.
Key Masters are a type of Master featured exclusively in The Legend of Zelda: Spirit Tracks. Unlike other Masters, they target an item, the Boss Key, and not Link himself. In that they are way more similar to Zant's Hands than a regular Master. Since they target Boss Keys, they only appears in dungeons where such keys exist. If they manage to steal the key, they will bring it back to its original position, forcing Link to try again.
Knucklemaster is a Master that serves as the Boss of the Skull Woods. Knucklemaster takes the form of a giant fleshy hand with an eye in its palm and protected by a gigantic iron gauntlet. Its main point is its eye and Link must trick it into slamming into the walls by fusing with them.