deriving from the popular phrase "pwn", sl0wn translates as the exact same, but to a lesser degree. sl0wning occures when one dominates the other team, but it is not as spectacular as a perfect victory. (say, 1 to 100 would be pwn, 45-100 would be sl0wn).
the litteral translation is "slightly pwned"
"i got sl0wned by a 12 yr old!"