runescapeclassic
The main RuneScape Wiki has an article on: Pure
The Old School RuneScape Wiki also has an article on Pure.

Pures are specialized account builds with the intention to PK. Pures keep certain skills high, while keeping others low. Pures are designed for special purposes, and usually try to maximize damage output at the lowest possible Combat level.

Pure Types

Minimalist

This type of pure keeps a minimal Defense level (1-10), with medium Attack (often 30 or 40) and high Strength, and do not train either Prayer or Magic due to their effects on Combat level. To further reduce their Combat level at the cost of Hits, some pures choose to use the wine trick to train their Attack, which allows even more Strength. As Armour bonus is not as important for these accounts, they may fill their inventories with more food or supplies which may provide an advantage when fighting other players in the Wilderness.

Prayer Beast

The Prayer Beast has similar classifications to the Minimalist, however also chooses to train Prayer for its combat boosts. A Prayer level of 31 is a very common choice, as it allows use of the Ultimate strength and Protect items prayers.

Flats

Flats train Attack, Strength and Defense equally, with Combat stats higher than if a player who has trained Magic and Prayer. However, the Rune plate mail body, Dragon axe, Cape of legends and Dragon square shield cannot be used by these accounts as they require Magic and Prayer as Quest requirements, unless the account is a Plate Pure. Many Flats accounts choose to use a Rune chain mail body and Klank's gauntlets rather than a Rune plate mail body due to the offensive boosts gained from the gauntlets.

Tank Mage

This type of account utilizes offensive Magic along with Defense to deal damage. Tank Mages cannot equip the Rune plate mail body, Cape of legends, the Gnome emerald amulet of protection, or Dragon square shield as these quests require stats in melee along with Prayer requirements.

Plate Pure

A variant of Flats that has access to the Rune plate mail body and Dragon axe without level 33 in Magic. These accounts were possible during RuneScape Classic's conversion to RuneScape 2 in 2004, as players could transfer Wormbrain's part of the map into RSC. Currently, the minimum Magic level to be able to complete Dragon Slayer is 31, using the boost from a Wizard's mind bomb to use Telekinetic grab.

Beneficial Quest Rewards

Rune Plate Mail Body (Dragon Slayer)

Gnome Emerald Amulet of protection (Tree Gnome Village)

Klank's Gauntlets (Underground Pass)

Gauntlets of chaos (Family Crest)

Dragon sword (Lost City)

Dragon axe (Hero's Quest)

Cape of Legends (Legend's Quest)

Dragon Square Shield (Legend's Quest)