Wiktionary
hostis humani generis
n. (context legal English) an "enemy of mankind", one who is beyond legal protection
Wikipedia
Hostis humani generis
Hostis humani generis ( Latin for "enemy of mankind") is a legal term of art that originates in admiralty law. Before the adoption of public international law, pirates and slavers were already held to be beyond legal protection and so could be dealt with by any nation, even one that had not been directly attacked.
A comparison can be made between this concept and the common law "writ of outlawry", which declared a person outside the King's law, a literal out-law, subject to the violence of anyone. The ancient Roman civil law concept of proscription, and the status of homo sacer conveyed by proscription may also be similar.