The story
Respelled clipping of generation five + -er, derived from genwunner.
Etymology from Wiktionary, CC BY-SA 4.0.
genfiver
Today it means: Someone who considers the fifth generation of Pokémon (BW and B2W2) the Pokémon franchise's peak in quality or the last good entries in the series, especially when elitist about the generations that came after. Full definition →