Alternate Beneficiaries, Generally
An alternate beneficiary is any person or entity that you want to receive a testamentary gift intended for a primary beneficiary who does not survive you.

Alternate beneficiaries also receive the gifts intended for primary beneficiaries who make a valid disclaimer or are categorized as slayers.

For Example:
Married couples with children often name their spouse as the only primary beneficiary of the residuary estate and name their children as the alternate beneficiaries.

See: Alternate Beneficiaries, Eligibility; Primary Beneficiaries, Generally