Blu-ray

Over time I have gained some knowledge of technology but was today completely thrown by something of which I had no knowledge at all. Staying with daughter to help post op, it was pouring with rain and there were two small boys to keep occupied, one of whom was being very grumpy after an inoculation yesterday.
I had wanted to see Paddington so decided to buy a copy and toddled out in the rain for a good walk. Found it in Smiths and was a bit taken aback when the lad at the checkout told me the price. He muttered something about blu-ray and I had no idea what he was talking about so ignored him. When I got back to the house, the DVD player refused to play the disk.
Where has this blu-ray thing come from? I had no concept of it and it looks as if I have wasted my money. DD has put it out for swaps on local Facebook sites, so we can live in hope.