You can give your sim new emotional traits like the drama queen trait, hobby traits like the ultra-popular gamer trait, or feminine and manly traits like the Homemaker trait or Woohoo lover trait. There are tons of defaults like the Anxious trait or Geek trait, and while there are some very good ones on the official workshop, there are loads more CAS traits to be found on the web. They define how you work, what kind of life you lead, and who may or may not like you.

Traits are one of the most important aspects of your Sim.