A Trap is a type of Challenge in exploration scenarios. Traps typically cannot Move. Most Traps are Hidden, only revealed through a successful Search or upon playing their first Action.
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 that are Hidden become revealed after playing their first Action (so the target suffers the usual penalties from visibility).
Traps have no EP totals and cannot be defeated through damage. They can be subject to effects such as Stat Track reductions, however, and they cannot generally play Reactions to prevent this.
Traps ignore rules for illumination and visibility, though targets may still suffer penalties if they cannot see the Trap.
Traps ignore water & swimming rules.
Traps start with a 0 in each Stat Track.
Traps are each worth half a PC of equal level.
See also: Creature, Environ, Obstacle, Seeker, Player's Guide Chapter 5: Exploration, DM's Guide Chapter 3: Running Scenarios