LLD = Low Level Dueling
There is a lot of intepretation of what constitutes LLD, and generally in dueling LLD you duel within level bands.
These bands usually correlerate with the levels at which you get skills.
You get normally LLD chars at levels 9, 12, 15, 18, 21, 24, 29 (Just before final skills) and 30 (depends on realm as to wether this is LLD).
LLD opens up several character types that cannot compete in higher levels duels, and also presents a challenge of getting obscene damage out of a level 9/18 character.
With the exception of Level 29 LLD is mostly dominated by melee characters as skills are thin on the ground and spells do very little damage. At level 29 a number of gear choices open up the possibility of making high damage caster characters - SOJ for example.