The term 'Hibachi Filler' refers to the type of fuel used in a hibachi, which is a traditional Japanese cooking device. The most common type of fuel used in a hibachi is coal, which is a five-letter word that can be used to solve the crossword puzzle. Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. It is widely used as a fuel source for both residential and industrial purposes.