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.