Gom jabbar is a torture hex (canon)[1] that spews a glob of a tar-like substance. Once stuck to a person, it cannot be easily removed. The tar burns the immediate area that it touches and continues to inflict pain on the victim. It is only seen when Draco uses it on Harry. This spell is considered advanced-level dark magic and caught severe attention from the Hogwarts staff, though Harry would not name his attacker.


  1. According to Professor Flitwick in chapter 24