Not to be confused with Drop Chance Rarity, officially known as Tier, is one of the factors of any item in SkyBlock. An item's rarity serves as a good description of its worth and usability. In the case of Armor, Weapons, and Accessories, rarity also affects how strong/costly a Reforging will be. Every item in Skyblock will come with a rarity, you might need to scroll down on the item description to see the rarity.
Common items are usually relatively easy to get from the start of the game and not very valuable, except for when sold in bulk. These items range in value from a seed, worth 0.5 coins and considered very easy to get, to a Diamond Block worth 72 coins and considered somewhat harder to get for an early-game player.
Uncommon items can be hard to obtain at the start of the game but become more common as a player progresses. These items range in value from a Diamond Pickaxe, worth 12 coins without enchantments, to an Enchanted Diamond, which can sell for about 1300 coins to the bazaar.
Rare items tend to be hard to get even mid-game, but quite valuable, and often necessary in order to reach the late-game. These items range from pieces of the Miner's Armor Set worth approximately 1,000-4,000 coins each, an Enchanted Diamond Block, which can sell for about 200k coins to the bazaar.
Epic items tend to be very valuable. Examples include late-game level armor and weapons like the Jerry-chine Gun, which is a powerful magic weapon, that commonly sells for millions without enchantments, and the Tier IV - Tier VII Perfect Armor pieces worth ranging from 4,000,000 to 8,000,000 coins when sold in the Auction House. These items can range from Dragon Fragments, some of which can be bought from the Bazaar for 2,500 coins, to the Overflux Power Orb, which sells for around 30 million coins.
Legendary items are some of the most valuable items in the game. This includes items ranging from the Bonemerang, which is worth over 25 million coins, to the expensive Hyperion, considered one of the best weapons in the game, that is over 400 million coins. Another example of a Legendary item is the Tier XII Perfect Armor, which has the highest defense - and with that, one of the highest EHP - in the game.
Mythic items are items that you can get by using a Recombobulator 3000 on a Legendary item to make it a Mythic one, or a level 9 enchantment book such as Infinite Quiver 9.
Supreme items are items that you can get by using a Recombobulator 3000 on a Mythic item to make it a Supreme one, or a level 10 enchantment book such as Feather Falling 10. Recombobulating a level 10 enchantment book will make it special.
Special items are usually limited-time items or items that only a select group of players currently own, and are usually only trophies or cosmetics. This includes the Game breaker which is given to players who reported a game-breaking exploit or glitch (like dupe glitches and server crashes) and the New Year Cake, which is given to everyone at the end of each in-game year by the Baker. This rarity can be obtained by Recombobulating a Supreme item.
Very Special items are Special items that have a Recombobulator 3000, which upgrades rarity, applied onto it. Although you can do this, it is more recommended to use a Recombobulator 3000 on armor and weapons.