What is the difference between "curd" and "yogurt"?
In India, curd is marketed as "yoghurt."
see http://en.wikipedia.org/wiki/Curd
Curd and Yoghurt are indeed used interchangeably in many parts of (mostly urban) India and the region in general, though probably not in the UK, the US and some other parts of the world. (Thanks to @Peter Shor for the guidelines).
This answer seems to do a good job of explaining the difference. Yogurt and curd are similar in that bacteria are used to produce lactic acid to thicken the milk. They're different in that yogurt is made with pure culture for consistency.