Recently, a story appeared in the news about some plastic-wrapped peeled mandarins for sale in Whole Foods. Whole Foods swiftly removed them and said 'our mistake'.
Here's the tweet that the BBC story used in its report:
Nathalie uses the term 'oranges' to refer to these fruits, which the story refers to as 'mandarins'. In my own native dialect, orange refers to something different from mandarin as well, with oranges being bigger, harder to peel, full of pips and generally a nuisance to eat. Clementines and satsumas are smaller but similar tasting, easier to peel and a much more pleasant experience. Mandarins are something I hardly ever eat, but they have a sharper, almost sour taste which is quite nice but very different again.
Many of the dialect differences I've experienced come from the time when we moved from Shrewsbury to Newcastle when I was 11, and this is one of them, although I don't think it's really a regional difference: I think that it just emerged through mixing with a different peer group. Plenty of my friends did call all these orange citrus fruits oranges, and I assimilated (though I still do make the distinction myself).
This kind of variation in the semantic coverage of a term is one that often causes great debate. A surprising one was tortoise/turtle. To my mind, it's easy: tortoises live on land and turtles live in the water. Americans (I thought) simply call all of them turtles. It turns out that not only is my classification of chelonians not quite accurate, neither is my classification of Americans (they vary! who knew?). I'm yet to work this one out fully, but it sparked a full-on twitter row last time I tried.
The most bitterly-fought battle is probably the one over what different kinds of bread should be called (buns, rolls, baps, etc.) but a related one is what counts as a sandwich. An effect of moving south a couple of years ago was that I would sometimes order a bacon sandwich in a takeaway place and get bacon between two slices of bread. Now stay with me, this is complicated. At home, or in a place where I'm sitting down to order a bacon sandwich, I expect this. But in a takeaway place, I expect it to come in a bun (bap, roll, whatever). In places round here, it seems that sandwich is more restricted in meaning, and covers only those made with sliced bread. You can have a roll, but you have to ask for it specifically. A bacon roll is a taxonomic sister of a bacon sandwich, not a hyponym of it (in other words, bacon rolls and sandwiches are two different examples of bacon-in-bread items, rather than a bacon roll being a sub-type of bacon sandwich).