A player's inventory is a term for all of the items they are carrying. The game interface splits the inventory into two sections: the backpack inventory and the equipped inventory.
The backpack inventory is where the player carries items that can't be or aren't equipped. A player's backpack inventory can hold up to 28 items, and any additional items must be stored in the player's bank. Some items are stackable (such as coins, runes, and arrows), which means they only take up the space of one item, no matter how many a player has.
The limit of 28 items in a player's inventory is integral to the RuneScape economy. Since only 28 items can be held at once, this requires players to make trips to banks to deposit items while they are gathering or making items. This adds time to the process of gathering items such as logs, ores, or flax and the process of making items, such as bowstrings, bars, and bows. If inventory was unlimited, the prices of such items could face a considerable drop because it wouldn't take as much time to obtain large amounts of them. Runecrafting would be made ridiculously easy, as players would be able to craft infinite amounts of runes in a single trip. Gathering skills, such as Fishing, Woodcutting, and Mining (particularly mining rune/pure essence) could be trained for infinite amounts of time without much movement, and processing skills, such as Smithing, Cooking, and Fletching would be extremely easy because infinite numbers of materials could be processing into finished items in one trip. The limitations of inventory help to stabilise the RuneScape economy.