Three times today I've read about the supposed 'Indian summer' that we currently have in UK. I'd always thought the term applied to extended sunny periods in October or later so (as usual) the journalists had it wrong ....
So I've done a bit of searching and it seems there are two meanings/derivations - one for Europe and one for North America. Indeed, looking in Wikipedia, there are several variants:
Indian summer - Wikipedia, the free encyclopedia .... that is all without what summer is like in India which is a large place and presumably the start, finish and nature of summer varies from North to South and East to West of the country: I'm sure Suhas K can enlighten us!