Straining is the only difference. Greek yogurt is thicker than regular yogurt and that is because the yogurt is strained after fermentation to remove more of the whey. This is great news if you are lactose intolerant, because you can reduce the lactose in your yogurt simply by straining it and turning it into a Greek-style yogurt. Personally, I strain all of my yogurt until it is very thick. I like it to resemble sour cream in thickness. I have found that chilling the yogurt prior to straining it does improve the yield.