Tier

Tier is a measure of your accumulated experience. A core character starts at tier 1. A tier 1 character is more than just a novice; you're reasonably accomplished and capable, on par with a college student or person in a typical job that requires some experience or training.

Over the course of the game, as you travel, experience things, and accomplish goals, you will advance to higher tiers and unlock new capabilities. Very experienced characters will reach Tier 6, and perhaps even higher. A Tier 6 character can accomplish a lot more than a Tier 1 character.