Non-player characters or NPCs are entities created and controlled by the game, in contrast to characters created and controlled by the players of the game. NPCs include any monster or race that can be targeted in the user interface.
A family is a group an NPC is associated with. This plays a role in Daily Kill Variety, Slayer achievements, and Slayer potions. On the wiki, race refers to the literal race or species of an NPC, such as a Crimson Moa belonging to the Moa race.
NPCs use profession skills and monster skills, with many monster skills that provide unique effects and animations. Monsters are not dependent on a weapon and do not have conventional skill bars like players. However, they must still use skills to attack, including normal attacks. Players can observe attacks that inflict damage through the "Combat" filter in the chat.
Most NPCs will have a level like players. In some cases, allies do not have a listed level. All NPCs that can become hostile, including neutral and hostile NPCs, will have a level. The level of a foe is used to calculate the amount of experience a player gains upon its defeat.
Most NPCs have one or more abilities that describe skills available to the NPC. These abilities are descriptive rather than definitive, any monster that has a skill that inflicts bleeding may have a "Bleeding" ability and some monsters that inflict bleeding do not have an ability related to bleeding at all.
Friendly NPCs are known as allies. Skills that apply healing, boons, or other effects within a radius can affect friendly NPCs in addition to other players.
Hostile NPCs are known as foes, enemies, mobs that will attack a player or allies of the player. Hostile foes are identified by red text in their name, targeting, and aggro condition.