An augment is a type of Gear equipped in the Augment slot, of which there is one. Augments commonly provide enhancement dice to the Action and Reaction entries of equipped Interaction Expertise. They are used exclusively in interaction scenarios.
Augments have a level requirement provided. A PC's level must be equal to or greater than the listed requirement in order to equip the augment. Augments typically have a Magic entry as well, which is used to add Magic cards to the interaction deck.
Augments also have an Extra Effect provided, which adds some additional flavor and fun when equipping the card.
For more information, see Player's Guide Chapter 7: Gear and Wealth.