Immediate family members, according to the law, include one's spouse, children, parents, grandparents, siblings, as well as one's in-laws. It also includes adopted children and stepchildren also are usually included in the definition. In some states, partners from same-sex marriages or civil unions also are considered immediate family.

The significance of being defined as an immediate family member can be seen throughout the law. Immediate family members, for instance, receive preference for immigrant visas. In some states, they cannot be completely disinherited, no matter the express language of a will. Federal law allows an employee 12 weeks of leave to care for an immediate family member's serious health problem.

As the definition of immediate family members expands (with the proliferation of civil unions, for example), and the benefits increase for these members, the temptation to abuse the system can be overwhelming.