It's pretty much THE smallest manufactured, powered, operating model railroading scale. The scale (or measurement ratio) is 1 to 220. That means a 40 foot long car is a little over 2 inches. The gauge (distance between the rails) is 6.5mm. Oh yes, it would be advisable to become accustomed to the metric system when working in Z scale! There aren't a lot of manufacturers producing products in this scale but there are enough to turn out quite a healthy variety to give a person a lot of options in selecting geographic location and historical period to model. There also aren't a lot of distributors and most hobby shops that carry "trains" don't stock Z. But there's often quite a lot on e-Bay including "stores" and there are a number of other shops running internet sites for purchasing online. Rather than be overly redundant, since there's a lot of other sites with more background and greater detail, I'll just refer you to the sites in my favorite links.