I looked up differences between Christmas carols and other Christmas songs. Generally about carols being about nativity or some other traditional songs not necessary religious while other Christmas songs are about things like love, loneliness, fun, celebration etc. set around Christmas time. But different sources don't agree on the exact definition.
I guess everyone agrees that Silent Night and some others are carols and that Stop the Cavalry (by Jona Lewie) is not. But then there's Jingle Bells. According to some sources it's a carol. It's traditional albeit secular and initially not allowed in churches. Many people agree it's a carol without even considering to question it. But other sources say it's not a carol as it's not about nativity. Then there's 12 Days of Christmas.
Is there a clear definition of a Christmas Carol? Who's the authority on what the definition is? (I'd expect the church.) Or is it loose and for some songs it's a matter of opinion?