From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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"