Waterfall: A visual display of radio signals (and other sounds) found on the tuned frequency.
High-end transceivers apparently come equipped with a water-fall display - something to do with improved spectrum visibility. This is supposed to lead to potentially higher QSO count and rate.
A waterfall display is a graphical representation of the signals across a frequency range, generally color-coded to indicate signal amplitude or strength, displayed over time.
Having an overview of all signals across a portion of the spectrum allows you to quickly and easily determine whether there are any strong signals, which usually indicates stations that would be easy for you to make contact with.
Not having to scan across the band to locate any station that might happen to be transmitting at the exact moment you pass over its frequency but rather being able to locate stations transmitting while you are working another station, means that you can immediately jump to the frequency when you are done with the previous station.
简而言之，瀑布图就是横坐标是频率，纵坐标是时间，依据不同颜色变化表示不同信号强度，即直观看出何种频率随时间变化的信号强度最高
此贴回答更为清晰。