a greeting,
something between a "hi" and a "hello"
josh: hiello, jock.
jock: washizile dizzle?!
hiello is a mix of two words hi and hello.
John: hiello Sarah!
Sarah: oh hiello John, how are you today
It is a mixture of the word "hi" and "hello" that is an enthusiastic way of saying one of those two words.
Hiello! How are you doing?