Are blocks in hand considered items?

Question

I am having difficulty understanding some differences between an item and a block. This is what I understand so far:

Inventory	Block	Item	Understanding
Stone	x		In placed position, it is a cube / block
Dandelion	x		In placed position, it takes up an entire cube/block area and nothing else can be placed on that coordinate
Iron Axe		x	It can only be in the player's hand; If the right click (or the set shortcut for placing blocks) is triggered, the axe is either used in a different function or dropped out of the player's hand

I am mostly confused about whether blocks are also considered items when it is not placed on a coordinate. For example, the block is in a chest, the block is in the player's hand, and the block is in a block with an entity (such as a cobblestone in a furnace). What exactly is considered a block and item?

Answer 1

If the block, isn't placed, it is an item. Anything you can pick up and store in slots of your inventory or a container like a chest is an item.

Answer 2

from the standpoint of the game's code, an "item" is anything within the player's inventory, or an Item entity (i.e., a floating item on the ground). blocks are the physical objects in the world you place and interact with; stone, crafting tables, beds, and so on are all blocks.

if you're talking from the standpoint of the player and their uses, anything you can place down and not just use is a block; e.g., you can place stone, but not a snowball.