While adventuring, characters (and sometimes their belongings) are affected by abilities and effects that apply conditions. For example, a spell or magic item might turn you invisible or cause you to be gripped by fear. Conditions change your state of being in some way, and they represent everything from the attitude other creatures have toward you and how they interact with you to what happens when a creature drains your blood or life essence.
A trait is a keyword that conveys additional information about a rules element, such as a school of magic or rarity. Often, a trait indicates how other rules interact with an ability, creature, item, or another rules element that has that trait.