Holy Oil
From Super-wiki
Castiel obtains some Holy oil from Jerusalem. It can be used to trap an angel by getting them to stand inside a circle of it and setting it alight. Meg was burned by the fire that trapped Castiel; it is unknown but one could assume that she died due the holy fire.
Contents
Uses of Holy Oil
5.03 Free To Be You And Me
Raphael is trapped by Castiel and Dean this way in . They leave him in the still burning circle.
5.08 Changing Channels
Sam and Dean use it to trap Gabriel, but later release him.
5.10 Abandon All Hope
Lucifer uses it to trap Castiel, but he manages to break the circle and escape.