freedom rider

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One of an interracial group of civil rights activists in the early 1960s who rode buses through parts of the southern United States for the purpose of challenging racial segregation.

Wiktionary

1. n. politics, public policy In the United States during the 1960s, a civil rights activist who participated in one or more bus trips, known as freedom rides, through parts of the southern U. S. to demonstrate opposition to racial prejudice and segregation.
2. n. politics, public policy A participant in one or more of the similar excursions undertaken by protesters in Australia during the 1960s, in opposition to unfair discrimination against Aborigines.

WordNet 3.0

1. n. one of an interracial group of civil rights activists who rode buses through parts of the South in order to protest racial segregation