freedom rider

Short definition from Wiktionary

Noun

1. 1
   In the United States during 1961, a civil rights activist who participated in one or more trips by bus or other forms of transport, known as freedom rides, through parts of the southern U.S. to demonstrate opposition to racial prejudice and segregation.
2. 2
   A participant in a similar excursion undertaken by protesters in Australia in 1965 in opposition to unfair discrimination against Indigenous Australians.