Pooled Experience
When you gain Experience Points (XP), the XP accumulates in an Experience Pool. When you train a skill (or skills), the XP is transferred from the Pooled Experience and into the skill being trained (which raise the skill's level).
There are two main types of Pooled Experience:
XP in the Producer Pool can only be applied toward increasing the level of Crafting Skills, whereas XP in the Adventurer Pool can only be applied toward increasing the level of Adventuring Skills