Alimony in solido (also referred to as lump sum alimony) is alimony in the nature of a final property settlement award that is not subject to change. It is an award of a definite sum of money to be paid in a lump sum or as installments over a definite period of time to make up for an imbalance in property division. It does not terminate upon the death of either party.
Per Tax Topic 452 on the IRS website:
Amounts paid to a spouse or a former spouse under a divorce or separation instrument (including a divorce decree, a separate maintenance decree, or a written separation agreement) may be alimony for federal tax purposes. Alimony is deductible by the payer spouse, and the recipient spouse must include it in income.
A payment is alimony only if all the following requirements are met:
For more information regarding Alimony please refer to IRS Publication 504 Divorced or Separated Individuals.