Adventuring Trainer
An Adventuring Trainer is a Skills Trainer that can train your Adventuring skills. Some can only teach you basic skills, advanced skills and master skills.
Trainers found in the Outskirts areas can only teach you basic Adventurer skills.
Trainers found in the various NPC Town's can teach you basic and advanced Adventurer skills.
The Master Trainer for each skill tree can only teach that skill tree, but can teach the entire tree. Sometimes a Master Trainer requires the completion of a quest to teach some skills.