ИМХО полное название investment interest expense limitation

Under pre-TCJA law and still under current law, interest expense that is utilized to create investment (non-trade or business) income is subject to the investment interest expense limitation of IRC Sec. 163(d). This limits the amount of interest expense that a partner in an investment partnership can deduct on his personal income tax return to the amount of investment income earned. For example, if an investor fund utilizes a margin account and pays interest on it, the fund will separately report this interest expense to its investors on the schedule K-1. The partners are then required to calculate how much investment income they have earned that year to determine if they can deduct the interest expense allocated to them. If a taxpayer is invested in multiple funds, they aggregate all of the investment income to determine if they can utilize the interest expense to offset their income. Although trader funds are considered to be in a trade or business, the income they generate is primarily investment type income. However, if the law did not specifically include the trader income in the definition of investment income, the interest expense utilized to generate trader fund income would be deductible without limitation. In order to bring parity in the investment world, Congress included in the definition of investment income, a limited partner’s share of a trader fund’s income, which then makes the interest expense allocated to a limited partner in a trader fund subject to the investment interest expense limitation. The interest expense allocated to the general partner of a trader fund is generally not subject to the investment interest expense limitation. This is because of the language in IRC Sec. 163(d)

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