In Wales it's also called a 'Twmpath' - pronounced (more or less) like 'toumpath'. The plural is something like Twmpathiau. A 'Twmp' or Tump is a mound or earthwork, often incorporated into a churchyard and often the site of dancing and merrymaking until the various chapels froze all the fun out of life.

I think the identity between ceilidh and barn dance gets closer the more southerly you get. In Scotland (around Edinburgh anyway) 'ceilidh' is more likely to be a fairly informal concert, ie with several short sets from a variety of performers, some of whom may play dance music and get the crowd on their feet, but usually without a caller.

Andrew