A named service listing credentials known to have appeared in breaches. A named tool rather than a concept.
Initialism for Have I Been Pwned, a breach-notification service created by security researcher Troy Hunt in December 2013; pwned is gaming slang for defeated or compromised, said to trace to a typo of owned on an early custom map.
A named service listing credentials known to have appeared in breaches: a named tool rather than a concept, kept for what it can warn.