These different names are used in different contexts, so you just need to pay attention and copy the examples that you hear. If you are reading out a long number (like a telephone number), it's easier to use "oh" for the zero. This is our natural option. Of course, if it's numbers and letters together, like a password, then you don't use "oh" for zero. Sport has its own set of "0" names. For football, you would say "nil", whereas for tennis you say "love". You might hear "oh" or "zero" for scores, but not "naught".

Zero is American English. Naught is British English. O is a letter, not a number. But people say O for zero all of the time here in the U.S. Sometimes it sounds better than saying zero.

With apologies to Jerry, it's a little misleading to say that 'Zero is American English. Nought is British English'. This would suggest that only Americans say 'zero' and that British English speakers only say 'nought'. This isn't true at all. In fact, 'zero' isn't American English. The digit '0' is 'zero', and this word is used all over the world ...US, Britain, Australia, everywhere. We use it in mathematics, mainly. The problem with 'zero' is that it's a slightly awkward word to say. It's not originally an English word, and it doesn't fit well into English sentences. We say 'zero' if we have to, but we generally avoid it. If '0' appears in a telephone number, for example we nearly always call it 'Oh', like the letter. This is quicker, easier, and more comfortable to say as part of an English sentence. Again, this applies to all English speakers, everywhere in the world. Here's an example. Just the other day, I had to read out a very long reference number over the phone into an automatic voice recognition system. The number contained several zeros, so when I began reciting the number I made a conscious effort to say 'zero', thinking this would be clearer. I think that I said 'zero' maybe once or twice, but then by the time I got to the end of the long number I realised that I was instinctively saying 'O'. If we see the number 560790, the most natural way to say this is 'five six O seven nine O'. 'Nought' - or 'naught' in American spelling - is an archaic English word meaning 'nothing'. Speakers of German and Dutch will recognise the Anglo-Saxon roots of this word. Yes, 'nought' is used occasionally in Britain, but not often. You should recognise this if you happen to hear it, but you will never need to use it. One of the few times it feels natural to use 'nought' is in the plural, for example, 'Did you say the reference number was 53008 (five three double O eight)?' 'No, in fact it's 530008. There are three noughts in the middle, not two.'

You're welcome, Isra