Passive income includes interest, dividend, royalty and annuity income for which you received a 1099 form. The 1099 shows what and whom you paid: taxes in Box 6, and country in Box 7.
The general limitation category covers your wages, salary and any highly taxed passive income. Income becomes "highly taxed" for IRS purposes when the foreign country's tax rate is higher than the U.S. rate. For example, if Country Z taxes your interest income at 50 percent, and the U.S. taxes it at 35 percent, the interest you earned in Country Z goes under general limitation income on Form 1116.
Section 901(j) countries are the five countries the U.S. has sanctioned. You must report earnings from any of them.
The lump-sum distribution category represents income you got from a foreign-sourced pension plan.
"Resourced by treaty" relates to tax treaties the U.S. has with other countries. You complete a Form 1116 for this category if the country in which you worked has a special agreement with the U.S. about how it taxes your income as a foreigner. Under "resourced by treaty" agreements, all of your income, including any money you made in the U.S., counts as income from the treaty country when figuring out the taxes you owe it.