An angel trap was a sigil trap and a means to trap an angel besides holy fire. Like another trapping methods, angels could not escape once inside the trap, but unlike holy fire, angels trapped by this could not use their powers.
Like its counterpart devil's trap, it appeared that no matter how powerful the angel, an angel trap still affected them. From an ordinary angel to higher-ranked angel like Gadreel, or an archangel like Lucifer.
One of the ingredients to safely summon and hold Lucifer was an angel trap arranged on the square base of a cage, and was created by the witch Rowena. While it was used to hold the archangel for a time, Rowena had slightly altered the sigils which allowed Lucifer to regain the use of his abilities, and apport Sam into the cage.