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:

• The spouses don't file a joint return with each other; 
• The payment is in cash (including checks or money orders); 
• The payment is to or for a spouse or a former spouses made under a divorce or separation instrument; 
• The divorce or separate instrument doesn't designate the payment as not alimony; 
• The spouses aren't members of the same household when the payment is made (This requirement applies only if the spouses are legally separated under a decree of divorce or separate maintenance.); 
• There's no liability to make the payment (in cash or property) after the death of the recipient spouse; and 
• The payment isn't treated as child support or a property settlement

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