Machin is one of those tremendous multi-purpose nouns - along the lines of truc, chose, fourbi, or bidule - that almost means what you need it to mean. Donnez-moi ces machins - pass me those thingies J’ai vu Monsieur Machin à la Poste, le mec qui travaille au bar - I saw whatsisname at the post office, the one who works at the bar