The item lookup system is how items are loaded from configs. It's designed to be extremely flexible and intuitive, allowing you to use custom items, blocks, entites, etc. wherever you want, without having to worry about what plugin they're from.
Anywhere you need to use items/blocks/entites, you can use this system. To look up an item, you need a key, and optional modifiers.
Available Lookups
Items
Vanilla Item item: "minecraft:nether_quartz"
EcoItems Item item: "ecoitems:mithril_sword"
MMOItems Item item: "mmoitems:dagger:1"
MMOItems needs more data: "mmoitems:category:item-id"