My father was a fruit broker, specialising in citrus fruit, specifically oranges. It's a broad category, encompassing a dozen or so different types. Even what we refer to as oranges can be broken down into specific types including Jaffa, Navel, Seville and Valencia (to name a few), all similarly sized but do differentiate in colour and taste.
Clementines were the smallest, followed by mandarins, which were a much deeper colour orange and had the most distinctive taste. Tangerines slightly larger, more yellow in colour. Satsumas, well, these are more commonly sold now as easy peelers. None of these things really taste as they once did and now are much sweeter than they used to be. This is entirely due to the power of the supermarkets who often demanded a uniformity, not just in size, but taste too. On the continent and in other orange producing countries, the range is still much broader and they still taste as they should.
Mandarins and clementines were more plentiful at Christmas, and my dad used to give everyone, from my friends parents to my teacher crates of them!