The term "White People" does not have a good definition, that's a fact. The US census includes everyone who is of European or Middle Eastern or North African origin, the UK census only includes Europeans, on the Internet you'll find anything from "Italians/Spaniards/Slavs are not white" to "Iranians are white". In the 19th century, Englishmen came up with the term and were excluding everyone except themselves as non-White (Irish, Germans, even Swedes were said to be "swarthy"). Jews can identify themselves as White or non-White, depending on what is more beneficial in any situation. The whole thing is ridiculous.
I think a compromise of the definitions would be: white is who is racially Caucasian and of Christian background (i.e. not Muslim or Jewish, but atheist is ok). This would result in the following peoples being "white", and I believe this corresponds to the intuitive labelling many people do.