Common:

The items most commonly found throughout a run

Uncommon:

Items with a small chance to drop from regular chests and a guaranteed chance from large chests and boss kills

Legendary:

Very rare items with a 1 percent chance to drop from chests unless opened from an orange chest

Lunar:

Items which you can buy from the bazaar or buds using lunar coins

Boss:

Items which have a chance to drop form bosses

Equipment:

Items which give you an additional ability but you can only hold one at a time