Here we generally consider a refurb to be a unit that's been gone thru by the manufacturer's service center, how thoroughly is always a question mark, tho. Most refurbs are based on customer returns to dealers from a conversation I had with one of the largest refurb sellers here in the US and generally were functioning fine at time of return (returned for a variety of reasons). It is provided generally here in the US with a limited warranty and resold in a slightly different box a new unit would be sold in, sometimes a specific retailer specializing in such (like our accessories4less.com) or even their own websites.
What happens in India you'll have to research with Yamaha, to see if this unit was sold thru one of their refurbishing programs (if they have one) or just some creative description from the seller. Just because it's sold thru Amazon by a dealer doesn't mean much except for how much Amazon will stand behind a return. Do you have consumer rules/laws about such?