@PJH said:
Better descriptions in this case would be "secondary sort key" and "primary sort key"; there is little reason to start splitting names unless you want to sort on family name rather than given name. The example given in the help article of a person with a single name, Simon, actually only has a given name (he used to have more names, but decided he didn't need them). Since most Western systems require a surname, he often ends up with his name in the field customarily used for surnames, possibly with a dummy "first name" (e.g. "S. Simon"). Other times it's "Simon No-Surname".(†) Note: leave first name blank if you do not have one. If you are not sure how to divide your name into the first and last name, read the Help article about names.I'm more intrigued by the concept of users without both a given-name and a family-name, and the fact they have an article about what to do if you don't have a given-name (not that they use those terms, of course, they use the rather ambiguous 'first' and 'last' name. They should have stuck to 'christian name' and 'surname.')
Many people prefer to use their second given name ("middle name") instead of their first (given) name. Some cultures have their names in a different order or have completely different conventions. For situations where you need to split names into bits and sort them, I've often wondered what the correct approach would be. I suspect the easiest correct approach would be to enter all the names in the order they appear in the full name and then specify the sort priority. That way, it doesn't matter which parts are patronyms, given names, family names or whatever.