In gaming, to trounce an opponent. To be "pwned" is to be defeated unmercifully. The term has also come to mean "hacked." For example, the website haveibeenpwned.com (HIPB) lists the top website breaches, and people can check to see if their email address was compromised.
Pronounced "pone," "pwen," "pawn" or "pun," the derivation of the term apparently comes from a common typo of the word "own" when typing too quickly "I own you!" On a QWERTY keyboard, the "o" and "p" keys are next to each other. See
hack.