The Free Speech Movement at the University of California, Berkeley was a 1960s student movement making headlines at the time and sparking the hippie counterculture on Earth.
While visiting Earth in 1986, James T. Kirk attempted to explain the erratic behavior of Spock to Gillian Taylor by saying that he believed Spock had used too much "LDS" during the 1960s while "he was part of the Free Speech Movement at Berkeley." (Star Trek IV: The Voyage Home)