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 good fanfiction; sexiness alone is not enough to illicit a true "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.