The term 'Western Sound Effects' refers to the sound effects used in films and television shows set in the American Old West. The most common sound effect is the 'MOOS' of cattle, which is a four-letter word. Other sound effects include the clomping of horses' hooves, the creaking of wagon wheels, and the crackling of campfires. These sound effects help to create an immersive atmosphere for viewers and evoke a sense of nostalgia for the Wild West.