A decibel is a unit of measurement that tells you exactly how loud a sound is. While a whisper is about 15 decibels, your neighbor's chain saw is about 120 decibels. Better invest in some ear plugs!
Because our ears are so incredibly sensitive to noise, the decibel scale has an enormous range. The 120 decibel sound of an airplane's jet engine is actually one trillion times louder than the very quietest sound your ear can hear. The word decibel, coined in 1928 by engineers in the telephone industry, originally measured the efficiency of a telephone circuit.