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 under divorce or separate maintenance decrees or written separation agreements entered into between you and your spouse or former spouse will be considered alimony for Federal tax purposes if: 

• You and your spouse or former spouse do not file a joint return with each other 
• You pay in cash (including checks or money orders) 
• The payment is received by (or on behalf of) your spouse or former spouse 
• The decree of divorce or separate maintenance does not say that the payment is not alimony 
• If legally separated under a decree of divorce or separate maintenance, you and your former spouse are not members of the same household when you make the payment 
• You have no liability to make the payment (in cash or property) after the death of your spouse or former spouse, and 
• Your payment is not treated as child support or a property settlement

You may deduct from income the amount of alimony or separate maintenance amount you paid, and you must include in income the amount of alimony or separate maintenance you received.

For more information regarding Alimony please refer to IRS Publication 504 Divorced or Separated Individuals.