Traps can appear on chests or on the floor in dungeons.
You can either use your conjurer's TRZP spell that costs 2 SP to disarm them, or your rogue can do it for free.
the TRZP spell is a lvl 1 spell so your conjurer will have it from the beginning. Also when used on the map it works for 30 feet, so 3 squares.
Disarm 50 traps on chests and in dungeons for the achievement.