• The Brandenburg test was established in Brandenburg v. Ohio, to determine when inflammatory speech intending to advocate illegal action can be restricted. 
• Detail: In Brandenburg v. Ohio (1969), the ‘clear and present danger’ test was expanded, and the ‘imminent lawless action’ test was laid down by the U.S. Supreme Court, which the court has followed since. This test states, “The constitutional guarantees of free speech and free press do not permit the state to forbid or proscribe advocacy of the use of force or of law violation, except where such advocacy is directed to inciting or producing imminent lawless action”. 
• The word ‘imminent’ used in the judgment is very important. Imminent means ‘likely to happen very soon,’ ‘at hand,’ or ‘fast approaching.’ 

Source: Article