Expertise is a type of Gear that comes in two categories: Exploration and Interaction, each used solely within their respective scenario. Expertise is equipped into the expertise slot, of which there are typically two. Equipped Expertise may be selected at the start of the scenario.
Expertise labeled generically as “Exploration Expertise” or “Interaction Expertise” does not require training to equip. All other Expertise requires training in the labeled classification. Training for Exploration type Expertise is commonly provided by a Craft, while training for Interaction type Expertise is commonly provided by a Profession.
For more information, see Player's Guide Chapter 7: Gear and Wealth.