The Rat Pack was a group of entertainers, including Frank Sinatra, Dean Martin, Sammy Davis Jr., Peter Lawford, and Joey Bishop, who were popular in the 1950s and 1960s. The term 'Rat Pack' was coined by Lauren Bacall in her memoir, referring to the group's reputation for partying and drinking. The crossword solution for the term 'Rat Pack' is 'LIES, ' which is a reference to the group's reputation for being wild and untrustworthy.