An item spawn is an exact location at which a specific item appears at regular intervals, free for any player to take. Although many item spawns are almost useless, some can be quite valuable. Secondary Herblore ingredients are often item spawns, such as snape grass or red spiders' eggs.
Some items are very fast to spawn, such as white berries, but others, like the sapphire spawn in level 46 Wilderness, are very slow. The regeneration of ores in rocks after they have been mined are similar to item spawns, as are a number of other mechanics such as tree growth in Farming.