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.
The rate at which an item reappears is dependent on both the item and the population of the current world. For example, nightshade will spawn once every 9 uses of the high alchemy spell on a very busy world, but only once every 18 on an almost empty world. Some items are very fast to spawn, such as white berries, but others, like guam leaves and 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; all of these are affected by the population of the world.