what does id mean in the context

{
    "replace": false,
    "values": [
        "modestmining:steel_nugget",
        {
            "id": "createbigcannons:nugget_steel",
            "required": false
        }
    ]
}
im making a datapack that adds tags to items so i can use them in crafting recipes and i wanna know what the id is for because its not for the tag given to the item