Can I give you the Scottish perspective? When I left Glasgow in the mid 60s, the term "country dancing" in Scotland, included both formal RSCDS and informal party dancing. Since then, probably in the early 70s, "Ceilidh Dancing" has been used to describe the party dancing. And "Scottish Country Dancing" refers to the formal RSCDS dancing. This was a good thing, as before that time I sometimes I turned up in my usual student clothes to a dance, only to find it out is was formal dancing. So the word "Ceilidh" now means mostly informal dancing and that's what I've liked to this day. Scottish Ceilidhs do not have Strathspeys - too formal. I was once told that English Ceilidhs came about at Cecil Sharp House when the then Scottish director used the term for an English barn dance there. I've yet to get that confirmed, but it would have been dated after the 70s.