Traits are a series of characteristics that are tracked by the game to reflect your character's behaviour throughout the RPG campaign. They're each divided into sets of pairs of opposites, as listed below.
Aside from some special cases, traits tend to be most influential when dealing with NPCs. If an NPC shares a particular trait with your character then they'll be more inclined to sympathize. NPCs with traits in opposition to your character will be less likely to sympathize, and hence will not get along with your character. This doesn't apply when traits are only weakly held by either party. So, if you only have a few points in a given trait, then there'll be no particular result.
You can select up to three traits to define the personality of your character. This portion of character creation is optional, so feel free to choose none if you don't want to bother with it.