slang To express excitement and enthusiasm about one's very specific and sometimes unpopular interest, especially by talking about it in great detail. My dad is a musician, so he totally geeked out during our trip to the Martin Guitar Factory. I completely geeked out when I realized I was looking at a sandhill crane—they're just so rare in this region! A: "Can I just geek out for a minute about how gorgeous Nicky Hopkins's piano playing is on this song?" B: "I don't know who that is, but sure?"