The Working Families Tax Relief act of 2004 has redefined "dependent." There are now two categories.
Qualifying child
Qualifying relative
A qualifying child is:
Your son, daughter, stepchild, adopted child, foster child, brother, sister, stepbrother, stepsister, or a descendant of any of them who:
Was under age 19 at the end of 2006 or under age 24 and a full-time student or any age if permanently and totally disabled.
Did not provide over half of his/her own support.*
Lived with you more than half of 2006.
A qualifying relative is:
Related to you or lived with you for the full year and who:
Is not a qualifying child of any other person in 2006.
Had gross income less than $3,200.
Is a person for whom you provided over half of his/her support for 2006.
The qualifying child or qualifying relative must also:
Be a U.S. citizen or national, or a resident of the United State, Canada, or Mexico.
Not file a joint return with his or her spouse unless the return is filed only to claim a refund and no tax liability would exist for either spouse if separate returns were filed.
You cannot claim a dependent if you can be claimed as a dependent by another.
* Support
In determining whether you provided more than one-half of an individual’s support (or that person provided over one-half of his or her own support), you can disregard any assistance received from the government or charitable organizations because you were temporarily relocated as a result of Hurricane Katrina, Rita, or Wilma.