The term 'Filled Shell' can be solved by the four-letter word 'Taco'. A taco is a traditional Mexican dish consisting of a corn or wheat tortilla filled with various ingredients such as beef, chicken, vegetables, cheese, and salsa. It is usually served with accompaniments such as guacamole, sour cream, and lettuce. Tacos are a popular street food in Mexico and are also widely consumed in the United States.