Extortion is the act of unlawfully taking money from someone using coercion - threatening psychical violence, destroying property, or setting pets on fire are a few of the more popular forms in my mind. In The Godfather II, extortion is a game mechanic, which nets you more money to hire more crew members in order to extort more money...it's sort of a vicious cycle, really. Thank goodness this sort of thing never happens in real life. Would be a pity if anything were to happen to all your nice stuff.