'Major Economy': Definition?

Media keeps saying India is the fastest growing 'major' economy. So which are really the fastest growing economies (regardless of 'major' or 'minor')?
1. Libya - 55% (GDP: $30 billion, #95)
2. Ethiopia - 8.5% (GDP: $70 billion, #65)
3. Vietnam - 7.7% (GDP: $200 billion, #50)
4. Ivory Coast - 7.6% (GDP: $35 billion, #90)
5. India - 7.5% (GDP: $2.5 trillion, #6)

The top 4 are all small countries. So it is easy to say "India is the fastest growing major economy". But is there any precise definition of 'major economy'? Where do you draw the line between 'major' economies and the rest? Do you take the top X economies as 'major'? In that case, what is X? 10? 15? 20? How much? Or do you take a GDP value as a cutoff for 'major' economies? And in that case, what is the cutoff? $ 1 trillion? That will translate to X = 15. Or is it some other value? Or should we take some other parameter?