Trap is a role for Challenges in exploration scenarios. Traps cannot Move and cannot be seen from adjacent unblocked regions. Most Traps are Hidden, only revealed through a successful Search or upon playing an Interrupt.
Traps function primarily through Interrupts, which tend to trigger from events such as a PC entering a region, playing an Action, performing a Search, etc. Many Interrupts on Traps then instruct the Trap to play an Action against the triggering PC.
Traps have no EP totals and cannot be defeated through damage. The can be subject to conditions, however, and they cannot generally play Reactions to prevent this.