ACLU means The American Civil Liberties Union
The American Civil Liberties Union (ACLU) is a nonpartisan, non-profit organization whose stated mission is to defend and preserve the individual rights and liberties guaranteed to every person in the USA by the Constitution and laws of the United States
It works through litigation, lobbying, and community empowerment. The ACLU has over 750,000 members and an annual budget of over $100 million. Local affiliates of the ACLU are active in all 50 states and Puerto Rico. The ACLU provides legal assistance in cases when it considers civil liberties to be at risk. Legal support from the ACLU can take the form of direct legal representation or preparation of amicus curiae briefs expressing legal arguments when another law firm is already providing representation.
When the ACLU was founded in 1920, its focus was on freedom of speech, primarily for anti-war protesters. During the 1920s, the ACLU expanded its scope to include protecting the free speech rights of artists and striking workers, and working with the National Association for the Advancement of Colored People (NAACP) to decrease racism and discrimination.
Source: Wikipedia