Sold = NPD and other third party estimates on data from select retailers massaging it with "shipped" numbers from releases from the video game companies.
Shipped = Release of numbers from the video game companies themselves.
There is a reason why we have this debate. Phanbois tend to take every "shipped" release of data from Sony, Nintendo, and/or Microsoft as the "truth" for what was "sold" during that month or quarter.
Those of us with half a brain would place more trust in the 3rd party sources like VGChartz and NPD, taking into account the biases of each 3rd party, because it is not a PR release from Nintendo, Microsoft, and/or Sony of "shipped" numbers to a bunch of middle-aged, yuppie investors who don't know a damn thing about video games, much less what "shipped vs. sold" really means.
Sold, if you want to get down to it is what every single retailer sells of a particular piece of hardware or software. Having this data would be perfect, but it is not reality because no one has the information from every retailer on every unit that is sold. The best we can do is dress it up in "estimates" with fancy graphs, statistical analysis, regression analysis and so on.
Shipped, is basically a "Hey look at me old white guy! I am doing just swell! Please pump more money into my company!"
So until we have a universities with statistic departments specializing in electronic entertainment market research and better tools from the point-of-sale to track every unit sold regardless whether it is sold in Timbuktu or Akron, Ohio, then we cannot agree.