grunneieren

I’m happy to write a wiki-style article, but I can’t locate a reliable, widely recognized definition for “grunneieren.” Could you provide more context (region, language variant, or a source where the term is used)? With that, I can craft a concise, neutral entry (under 300 words). If you prefer, I can also produce a neutral stub noting that the term is obscure and outlining possible regional interpretations, pending more detail.