Code H. Net investment income tax. 

This amount is the beneficiary's adjustment for section 1411 net investment income or deductions. Enter this amount on line 7 of Form 8960, as applicable. See the Instructions for Form 8960.

....And I think you meant Line 5, Part III (not II)

The amount reported in this box is your distributive share of royalties, annuities, and other income that isn't subject to the passive activity rules. It also includes income in respect of a decedent (IRD), which isn't included in box 1, 2a, 3, 4a, 6, 7, or 8.

My guess is that the trust received a distribution from an annuity or retirement account.