Deductions & credits

It was by process of elimination:

General Category Income General category income is income that is not section 951A income, foreign branch income, or passive category income or does not fall into one of the other separate limit categories discussed later. In most cases, it includes active business income and wages, salaries, and overseas allowances of an individual as an employee. General category income includes high-taxed income that would otherwise be passive income. See High-taxed income, earlier, under What is not passive income. 

Passive income. Except as described earlier under Income from controlled foreign corporations and Partnership distributive share, passive income generally includes the following. • Dividends. • Interest. • Rents. • Royalties. • Annuities. • Net gain from the sale of non-income-producing investment property or property that generates passive income. • Net gain from commodities transactions, except for hedging and active business gains or losses of producers, processors, merchants, or handlers of commodities. • Amounts includible in income under section 1293 of the Internal Revenue Code (relating to certain passive foreign investment companies). If you receive foreign source distributions from a mutual fund or other regulated investment company that elects to pass through to you the foreign tax credit, in most cases the income is considered passive. The mutual fund will provide you with a Form 1099-DIV or substitute statement showing the amount of foreign taxes it elected to pass through to you.

What is not passive income. Passive income does not include any of the following. • Gains or losses from the sale of inventory property or property held mainly for sale to customers in the ordinary course of your trade or business. • Export financing interest. • High-taxed income. • Active business rents and royalties. • Any income that is defined in another separate limit category.

IRS Publication 514