It means, living with you in your home as a member of your household, wherever that home happens to be. Note that if the child lived in your home more than half the year (6 months plus 1 day), select 7 months or higher, since the program interprets "6 months" to be "exactly half the year" and that can affect certain issues. And, there is a special rule for newborns, if the child has lived in your home more than half the time since they were born, select "the whole year" or 12 months.
This question relates to when parents are separated or divorced and live apart sharing custody. If you live with the child and the other parent in the same home (either married or unmarried living together) you should generally just say "the whole year".
