'Celtic Music' is a label invented for the convenience of record stores that have a too large collection for to use but the single label 'folk music' and a too small collection for labels like 'Altan', 'Barachois', 'Chieftains', 'Dubliners',...
I personally wouldn't use that label but it may help a search if you know what type of music to expect under that label.
Lately, I looked for Barachois in my local store (many thanks to that Mudcatter praising this group). They have a too large collection for a label like 'Celtic Music', so in the many shelves labeled 'World music' they have the subcategories 'Irish', 'Scottish' (including English, of course), 'North American' and many others. I failed to find Barachois under 'North American' and asked a clerc. 'Why? They are right there under 'Irish', second letter'. 'But they are from Canada' I insisted. 'But they play Irish music.'
You see, these labels can be convenient, if you know what they mean, nothing else.

Wolfgang