Drops, also known as monster drops or loot, are the items monsters leave for the killer when they are defeated or die. Drops can be picked up by players. Drops often include bones, coins or other items. A lot of monsters have "100% drops", which is an item or items that are always dropped by that monster. 100% drops are more commonly bones or ashes. Certain monsters have more than one type of 100% drops. A good example of monsters who have more than one type of 100% drops are metal dragons, who drop bones and also, metal bars of the type of metal they're made of.
Large monsters (that take up more than one square) will always drop their drops in the south-westernmost square. This also applies to any Ranged ammunition that falls to the ground when ranging those monsters.
The player who has done the most damage will see the drop before the other players. If a player has done half of the monster's Hitpoints in damage, and the monster has had time to heal, someone else may end up doing the most damage.
A delay between the damage being done, and the creature eventually being killed, does not seem to affect the person who sees the drop first, as long as they did more than half of the total damage done.
In very rare occasion, when right-clicked the exact same moment as the monster dies, a screen may appear with the 100% drop only (and arrows if Ranged is used) and not with the other drops. Then, if right-clicked on the same spot again, the drops are present. This shows that RuneScape first lets the monster drop its 100% drop, and then quickly calculates the other drops and then they appear too. To improve the chance for this to happen, log on to a world with low ping.
Drops will remain on the ground for 200 game ticks (2 minutes or 120 seconds) before disappearing. Drops are invisible to other players for the first 100 game ticks (1 minute or 60 seconds), after which time, anyone will be able to see (and take) the item if it is tradeable. The only exception is that if a player manually drops a non-food item in the Wilderness, it will instantly appear.
All items have a chance of being dropped that is expressible as a number—their drop rate. Drop rates are not necessarily a guarantee; an item with a drop rate of "1 in 5" does not equate to "This item will be dropped after five kills." While each kill does nothing to increase the drop rate itself, it is trivial to state that more kills gives rise to more chance overall.
Random number generator
The random-number generator (or RNG) functions similarly to drop rates. It generates an unpredictable, random sequence of numbers, thus denoting a random chance. For example, if you kill a lizardman shaman, there's a 1 in 5,000 chance it drops a dragon warhammer, so a function object, such as a die, has a 1 in 5,000 chance of rolling on 5,000 each kill, which would result in receiving the drop.
When a monster dies, it will roll most of its drops tables to see if a player should obtain an item, and then which item they should obtain.
These are the items that a monster is guaranteed to drop when it dies. Items on this table are usually remains, such as bones or ashes, but there is no strict limitation to what can appear on this drop table. While all items on this table have a drop chance of "Always", not every item with an "Always" drop chance is a 100% drop; i.e., some items, such as some quest monster drops, are guaranteed as a drop on the first kill, but are not obtainable afterwards. This distinction keeps one-off items from being classed here; such items are usually tertiary drops.
The main drops table, if a monster has one, is guaranteed to be rolled when a monster dies. It contains a selection of items, with one randomly chosen. For a small handful of monsters, this table can be rolled multiple times in one kill.
Tertiary drops, such as mysterious emblems, ensouled heads, and metamorphic dust, for example, are a separate table that is rolled for alongside the main drop. Unlike the main drop, multiple tertiary drops can be obtained in a single kill; however, similarly classed items cannot be obtained at the same time; e.g., if a curved bone is obtained as a tertiary drop, it is impossible to also obtain a long bone, but this roll will have no effect on obtaining a clue scroll.
Rare drop table
The rare drop table is an extra table of drops that can be rolled if a drop slot indicating it is rolled on the main drop. As such, the rare drop table drop will count as the main drop. The items available on the rare drop table are the same across every monster.
Universal drops are a class of items that can be obtained by nearly every monster, namely revenants. Currently, revenants are the only monsters in Old School RuneScape that share the same drop table.
Unique drops are drops that are unique to a particular monster. In other words, they are dropped exclusively from that monster. For example, pets, Fremennik rings, and Wilderness rings are unique drops.