"Swatting" (short for SWATeaming) refers to one user sending in a malicious and false report to the police of an imminent violent situation at the location of another user. The malicious user hopes that the police will respond to the reported danger with force, and endeavors to harm the victim through the violent harm, property damage, and psychological distress that interactions with armed police can instigate.
Swatting is one of the rare forms of internet abuse that has frequently led to the death of its victims, and been actively prosecuted when the perpetrator can be determined.
Though swatting grew out of gaming communities, it is now used in more ideological and political contexts. It is one of the main reasons that posting the physical location of another user (Doxxing) is such a significant threat, because it is a mechanism by which a user can threaten another user's physical safety from anywhere in the world.