The only possible verbal reaction after watching, reading, or hearing something emotionally intense. Often applies to song lyrics. Can apply to fanfiction, but only very goodfanfiction; sexiness alone is not enough to illicit a true "guh."
She understands the character so perfectly that it's heartbreaking. Reading it, it's just...GUH.
Guh means that yu are blown or you have no respaonse to something crazy or weird that happened. For example if you saw a unicorn in the middle of the desert you wouldnt know what to do or say besides wat the fuck.