Low level duel
From Diablo Wiki
LLD or Low Level Dueling is the practice of PvP combat between characters at a pre-determined level. Some players also refer to Very Low Level dueling (vLLD) or Medium Level Dueling (MLD), with level limits varying from game to game, but always set based on some threshold of skills or equipment options.
The point of LLD is to level the playing field and limit player tactics. Some classes are better than others at higher levels, and high level dueling is incredibly expensive, in terms of the equipment required and the time that must be spent to level up characters, find gear, etc. LLD gives a fun PvP outlet that doesn't require a character with hundreds of hours of play time. (Though acquiring the gear for a successful LLD character is still a lengthy process.)
The most popular LLD threshold in Diablo II was at level 9, though the term was generally applied to any character up to level 30. Level 9 was the lowest level a character could be and engage in PvP, and that level worked well since there was a fairly wide variety of equipment available, and characters had enough hit points and mana to use some tactics, while the vast majority of game items were still out of reach.
 LLD Gear
Though a quality LLD character doesn't require as much time to create as a max level dueler, serious LLD players put a great deal of effort into their creations. The trick is to find or create the best gear that can be used at a given Clvl. A normal Clvl 9 character who is using what they've found will have zero chance of winning a duel with a well-equipped LLD character, who will usually have been rushed all the way through Hell difficulty, to gain the quest rewards (more skill points and stat points) on all three difficulty levels.
LLD dueling is largely about equipment, and finding and assembling the best gear for a particular Clvl and skill is an enduring challenge to LLD players.
The best LLD gear in Diablo II was generally the best item with a lot of sockets, since jewels (and to a lesser extent runes and gems) could provide the most bang for the buck, with a low Clvl requirement. This was especially true for Clvl 9 duelers, since armor, weapons, and helms with 3 or 4 sockets (especially when filled by Jewels with +damage) could vastly out perform any other equipment options.
 Diablo III LLD
Nothing can yet be said about low level dueling in Diablo III, since we don't know enough about the equipment requirements or even the level requirements for playing in the Arena. The skill tiers are closer together at the low levels in D3 than they were in D2, so characters of even Clvl 10 will have far more skill options to choose from than low level chars did in D2.
- D2 skill tiers: 1, 6, 12, 18, 24, 30.
- D3 skill tiers: 2, 3, 6, 10, 14, 20, 26.
Traits will probably prove to be a major factor in D3 LLD, since they have such substantial passive bonuses.
The D3 devs have talked about low level item requirements a bit, and said that Gems will not have any Clvl requirements at all and should be useful for twinking. That might be a shame for LLD, since as powerful as the mods should be on high level 14 gems, low level dueling might become entirely a battle of which character has more big gems in their equipment.