Can effectively be translated as "vomit-inducing cuteness" or "so cute that I want to vomit." Can also be translated as "disgustingly cute." It comes from the two words げぼ (gebo), meaning to vomit, and かわいい (kawaii), meaning cute. Popularized by Kiryu Coco in her streams and was also used as a member emote.
▸ "I can definitely say that she's so gebokawa."
▸ "The one and only gebokawa dragon girl!"