An onomatopoeic term to refer to fangirling/fanboying; specifically, referring to the high pitched squeal a fangirl/fanboy often makes when fangirling/fanboying.
May also refer to a similar reaction common amongst teenage girls when their crush asks them out, displays interest, or even talks to them.
Megan: Oh my gosh! You know Josh, the lead singer from insert band here?! He mentioned me on his twitter account!! Iieeee!