<p>To be considered a legacy one has to have a parent or sibling at the undergraduate school to which they are applying. Having a father for example who attended Columbia College when you are applying to Columbia College is considered a legacy. One is not a legacy if they apply to Columbia College and their father went to a graduate school there.
If one has a grandparent who graduated from the undergraduate school and has been very involved in the school financially or in other ways over years, that is usually also considered a legacy even though Columbia indicates it is just siblings and parents.</p>