When I was a child, I'm pretty sure that Father Christmas (not Santa) brought a satsuma, not a tangerine. I love satsumas. I buy bags and bags of them when they are in season, and eat them until I start feeling really quite orange. It's surprising, but sort of charming too, that in an era when you can buy all sorts of fruit out of season all year round, the Season of the Satsuma is so short.
What I think of as a satsuma is Citrus Unshiu and although that Wikipedia entry doesn't mention it, I'm sure I've read an article saying that this particular fruit is disproportionately popular here in Britain, where we like the sweetness and the ease of peeling, and have less stern and demanding tastebuds than other nations who apparently are more likely to prefer more subtle and less sugary citruses. So, we give them at Christmas: hence the 'Christmas orange' name.
What I think of (and I *think* generally what greengrocers and supermarkets sell as tangerines, is Citrus Tangerina - a pleasant enough fruit, but not quite so easy to peel, and the skin has a different texture and flavour (I like the skins too!)
Santa or Father Christmas?
The really vital question: Satsuma or Tangerine???
Incidentally, I just learned from that Wiki article that a mature satsuma tree is hardy down to -9C. -9! It NEVER goes to -9 here. I wonder how much frost protection they need before they get big....?