Basically Iliy means I like you, but in a shorter more secretive way.
It's pronounced as what each letter is.
Such as if someone said, "Hey, Jen, Iliy." Them meaning Hey Jen I like you.
How you respond to such a term would be, "Iliy2."
Also you can respond to this term as, "Keou." This is basically taking the missing words out of Iliy (I LI KE Y OU) and using them as if you were finishing what they were saying. Cute right?