Many races have a level adjustment (commonly referred to as LA). This affects their maximum ECL (Effective Character Level).
The more powerful the race, the higher the LA.
What does this mean?
Basically on SCoD, the maximum level you character can reach is 30 - LA. So, if you are an Aasimar, with a LA of 1, then maximum level you can reach is 30 - 1 = 29.
ECL is the sum of your class levels (or Hit Dice) with your LA. So, an Aasimar Fighter 5 has an ECL of 5 + 1 = 6.
ECL is important when taking into consideration things like XP rewards and monster spawns, as they are based on ECL rather than total class levels (or Hit Dice).
However, in order to make getting started with high LA races, XP adjustment and monster spawns based off LA are slowly added, rather than applying the full value from first level. Basically 1 LA is added per level gained until max LA is reached.
To explain this better, consider this table for a LA5 race:
|Class Levels||ECL||Adjusted ECL|
|1||6||1 + 0 = 1|
|2||7||2 + 1 = 3|
|3||8||3 + 2 = 5|
|4||9||4 + 3 = 7|
|5||10||5 + 4 = 9|
|6||11||6 + 5 = 11|
So, as you can see, as the race reaches 1 level higher than their LA, ECL and the adjusted ECL reach parity. Prior to that the full penalty of being a high LA races is not in effect. This makes also finding low level grinding partners easier, as XP from kills is not so badly impacted.