Martin,
This is not a troll (trawl?). If it were, I wouldn't use my own name. I tried Sorcha's link and found myself listening to tunes I grew up with, two jigs called "The Frost is all Over" (featured on one of the Chieftain's albums) and "Saddle the Pony." These two tunes are played widely all over Ireland and form part of the vast corpus of music known as Irish Traditional Music. (The "Irish" is only used outside of Ireland as everybody knows what Traditional Music is inside Ireland). Never in all my wide experience have I heard of Ulster Scots Music until recently.
It is for this reason that I look for a definition. I was never aware during all the years when I competed in Traditional Music competitions in Ballymena Town Hall or at Fleadhanna or Céilís throughout the North did I ever hear the term used. There was -and still is- a great two way traffic in music between Scotland and Ireland but the joins are seamless for the most part in this musical continuum.
I ask again: can anyone define Ulster Scots Music in such a way that it is instantly recognisable as something distinct from both Irish and Scottish Traditional Music?