Source : Webster's Revised Unabridged Dictionary (1913)

Mixed \Mixed\, a.
   Formed by mixing; united; mingled; blended. See {Mix}, v. t.
   & i.

   {Mixed action} (Law), a suit combining the properties of a
      real and a personal action.

   {Mixed angle}, a mixtilineal angle.

   {Mixed fabric}, a textile fabric composed of two or more
      kinds of fiber, as a poplin.

   {Mixed marriage}, a marriage between persons of different
      races or religions; specifically, one between a Roman
      Catholic and a Protestant.

   {Mixed number}, a whole number and a fraction taken together.
      

   {Mixed train}, a railway train containing both passenger and
      freight cars.

   {Mixed voices} (Mus.), voices of both males and females
      united in the same performance.

Source : WordNet®

mixed marriage
     n : marriage of two people from different races or different
         religions or different cultures; "the families of both
         partners in a mixed marriage often disapprove"