hy is simply the phonetic abbreviation of the commonly used greeting "hi", and as far as i know has its origins in the GNAA, or at least that's where it seems to be used most commonly. As seen below it is frequently accompanied by the acronym "LOL".
by SATANIC JIHAD ALLAH IS GREATEST May 15, 2006

hell yea, hellz yea, heck yes, etc. Computer slang shorthand ive run across a few times and seems to be being used more often.
by Mark Weizbox February 24, 2005

“how’d you sleep”
by curious eloquent December 14, 2019

by Hy D. October 1, 2008

"Hy", the acronym most people scarc(e)ly use as "hello", or "hi". It can also mean "hell yeah, hell ya, hell yea". I'm sorry for my bad spelling, :(.
by -=:/Teh Alex\:=- December 28, 2005

by hyperbola November 2, 2010

'hitler's youth'
the generation of modern kids (teens) that follow in the footsteps of german dictator Adolf Hitler.
the generation of modern kids (teens) that follow in the footsteps of german dictator Adolf Hitler.
Jan: hey, are you still HY?
Mark: nah im over that
or
Jan: hey what is that scar on your chest?
Mark: it's a swastika i carved into myself cause im HY.
Mark: nah im over that
or
Jan: hey what is that scar on your chest?
Mark: it's a swastika i carved into myself cause im HY.
by jennipher renee June 30, 2009
