Pure is a word used within RuneScape to describe an account. It often refers to the target (or goal) of the player, having an objective to do well in only combat or only skills. Being a pure has it's advantages and disadvantages depending on what type.
Combat pures focus on training certain skills that they hold most relevant for successful combat and are usually made for kill (PKing). The purpose of keeping an account "pure", i.e. refraining from training combat skills which are considered less effective or irrelevant for the concept of the account, is to keep the combat level as low as possible in order to excel against players of a similar combat level in PvP. Some combat pures tend to generally neglect non-combat skills, although many will train a money making skill such as Woodcutting or Hunter to be able to buy equipment or to meet quest requirements for a combat-related reward such as Ancient Magicks, or the bonuses offered by certain Skill Capes (Prayer Bonus, i.e.). Agility can also be a very vital skill while fighting in the Wilderness (however, the equipment of pures is often very light). Pures who decide not to train noncombat skills are often at a huge disadvantage against other pures.
Combat pures are most commonly offence-oriented with high values in one or two offensive skills (Attack, Strength, Ranged and Magic), while having only minimal values in defensive skills, such as Defence, Prayer and/or Constitution. Such pures rely on a fast damage rate and/or a high max hit for quick kills, often catching their opponents off guard. However, there are also defence-orientated pures and pures that combine certain offensive and defensive aspects while neglecting others. There are a variety of combat skill combinations which may be considered favourable for different tasks and different types of opponents.
Due to a certain renown associated with combat pures within the RuneScape community, another motive to create a combat pure may be the prestige and/or the self-imposed challenge. Pures with unusual combat skill combinations may also be players experimenting with new combat concepts.
A skill pure or skiller is a player that develops non-combat skills more often than combat skills. The amount of time spent developing non-combat skills rather than combat skills can vary.
Skillers are often criticized for being "pointless" as compared to building up the same level of supporting skills on a combat character, although the choice of a skill pure is a self-imposed challenge. Most skillers are aware that not training combat does significantly limit the amount of quests they can do in the game, as well as the places they can explore, and to aid this some skiller accounts are side-accounts and not main ones.
A quest pure is a player who does all the quests while maintaining lowest possible combat level required to complete all quests while accepting quest rewards for combat skills. They also get all skills up to the required level to complete all quests. Quest pures can also use their skills to complete Achievement Diaries, to be even more impressive.
However, their effort can easily be ruined by new quests that give unwanted combat experience or with higher combat skill requirements. Since the rewards of incoming quests are unpredictable, it is expected that even the most successful quest pure must move on to a higher combat level soon after getting their achievement.