The term 'Fizzling-Out Sound' can be represented by the crossword solution 'PFFT', which is an onomatopoeia for a sound that is quickly fading away. It is often used to describe a sound that is quickly dissipating, such as a balloon deflating or a firework fizzling out. It is also used to describe a situation that is quickly losing momentum, such as a project or idea that is quickly becoming irrelevant.