The Collaborative International Dictionary of English v.0.48:

Mixed \Mixed\, a.
   Formed by mixing; united; mingled; blended. See Mix, v. t.
   & i.
   [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mixed marriage
    n 1: marriage of two people from different races or different
         religions or different cultures; "the families of both
         partners in a mixed marriage often disapprove"