Hard assets such as investment real estate can provide an investor with both capital gains and, I believe you meant investment income. Numerous assets classes, depending on the investor's state (country or geographic area) and that area's tax laws will have significant, and often changing consequences for each type of investment.
However, keep in mind that capital assets are defined by the U.S. IRS as property such as home or car, and ohter investment property such as stocks or bonds.
Several definitions to keep in mind include capital gain or loss, the difference between price paid and price sold (occasionally including holding and selling costs, etc.). Your basis in the investment property is what you paid for the asset.
Hope this helps...never heard of interested income, but I don't know everything either. )