I think that is more a language or translation question. I do not know if there is really a difference between these two words in UK or USA. For me a "standard" is more a guide or a rule of thumb while a "norm" is something binding. But I think in the english speaking world it is just the opposite because it is called "ISO standard" and not "ISO norm".

the word "standard" as used in "ASTM standard" or "BS standard" has exactly the same meaning as "norm" as used in "DIN norm" of "norme AFNOR". it means a more or less exact description of a test, sizing of screws, diameter of bearings or any other phenomenon that lends itself to a clear description.

As far as ISO 68 is concerned: it is a viscosity specification that says that a oil meeting ISO 68 must have a kinematic viscosity at 40 degrees Centigrade of 68 mm2/s +/- 10%. The ISO range is defined within a certain ISO standard and various national standards are derived from this standard and thus you may find the request for a ISO 68 oil based on a ISO, AFNOR, DIN etc standard - meaning exactly the same thing.

The purpose of the ISO standards is to get more or less globally accepted standards which make it far easier to import and export manufactured goods.

If you compare the Turkish and the French norm for ISO 68 you will notice that in the end they do describe the same thing.

If you look into national standards/norms you may notice that these are increasingly based on ISO standards.