a loving term to grab the attention of someone; something you say when you want something; could mean simply "i love you"; a way of expressing happiness or confusion; just a wonderful term.
BOY: I love you too.
FRIEND ONE: ishnoo?
FRIEND TWO: yeah, I like this song too.
PERSON ONE: ishnoo!
PERSON TWO: HIIII!!
CHILD: (gestures to radio) ishnoo!
MOM: yeah, you can change the channel.