Item stack
An item stack is a collection of multiple items of the same type. Any item type has a stack limit, it is not possible to stack more items of such an item than the stack limit.
Appearance
Item stacks be stored in inventories and can also appear in the world itself.
In an inventory
In the inventory, item stacks are represented by an icon and optionally a number. The number is the size of the item stack. If there is no number, the size is 1. Refer to Inventory#Controls for instructions how to use item stacks in inventories.
In the world
In the world, item stacks are also represented by some sort of symbol. For blocks, the icon is a rotating mini-version of it. Basicly everything else is represented by the inventory icon. Item stacks can appear for several reasons in the world: You drop them, you tried to mine something but your inventory is full and for several other reasons. If you see an item stack in the world, you can collect it by pressing the attack key (left click usually) on it. It will appear in the player inventory if there is enough space. In the world, any item stack appears as if it is just one single item. It is not possible to see the size of an item stack until you’ve collected it.
Item stacks in the vanilla Minetest game
All tools and weapons have a stack limit of 1. All other items have a stack limit of 99.
Item stacks in other games
Other games can set the stack limit freely for all items. It defaults to 99 for ordinary items and to 1 for tools. It is unlikely, if not impossible for tools to have a different stack limit.