Rarity is based on drop rate, accessibility, and value. This wiki assigns five normal ranks and three special ranks. You can check the loot table also.
These values are only approximations meant to give a general idea of the rarity of items and are in no way hard coded into the game.
Very common items can be obtained by all players and are extremely abundant. A club is a very common item.
Uncommon items may be difficult or impossible for a new character to obtain. Items in this category and up tend to be more valuable to other players than to shopkeepers. Most are worth at least 500 gold to players. Tier two scrolls and large axes are examples of uncommon items.
Very rare items are the most difficult items to obtain in Aberoth. They are generally worth at least 100,000 gold, and some may trade for more than a million. Examples of very rare items are the +2 attack ring and any of the bone shields.
Seasonal items can only be obtained on certain days of the year, such as December 25. The snowball is an example of a seasonal item.
Unobtainable items are items which cannot normally be obtained or may not be kept after logging out. In addition to some glitched items, the orc prison key in the game's introduction is unobtainable.
Discontinued items are items that were available in the game at one time but no longer exist as membership rewards or drops. The Medal of Gratitude is an example of a discontinued item.