What does it mean to "redefine" marriage?

See video

Jennifer Roback Morse, Ph.D. answers a caller who claims that allowing homosexuals to marry will not effect the overall institution of marriage. 

Jennifer Roback Morse, Ph.D. is the founder and president of the Ruth Institute, a project of the National Organization for Marriage to promote life-long married love to college students by creating an intellectual and social climate favorable to marriage.  She is also the...