To temporarily enter techno-nerd mode while in a non-hackish context, for example at parties held near computer equipment. Especially used when you need to do or say something highly technical and don't have time to explain: "Pardon me while I geek out for a moment."
See computer geek, propeller head.
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Nearby terms: gedanken « geef « geek « geek out » GEI » GE Information Services » GEM