Per IRS Publication 501 Dependents, Standard Deduction, and Filing Information, on page 10:

Dependents

The term "dependent" means:

• A qualifying child, or
• A qualifying relative.

On page 11:

Tests to be a Qualifying Relative

1. The person can't be your qualifying child or the qualifying child of any other taxpayer.
2. The person either (a) must be related to you in one of the ways listed under Relatives who don't have to live with you, or (b) must live with you all year as a member of your household (and your relationship must not violate local law).
3. The person's gross income for the year must be less than $4,300.
4. You must provide more than half of the person's total support for the year.

See IRS Publication 501 for exceptions to the qualifying relative tests.

Additional Information

For more information on qualifying children, see Dependents - Rules For Claiming. For instructions on how to enter dependent information in TaxAct, see Dependents - Adding in Program.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.