A Dotcom-Monitor Waterfall Chart is a bar-chart type data visualization that sequentially displays both the individual performance and cumulative effect of individual webpage-elements loading in a browser. 

Waterfall Charts are generated as part of a performance report, and are accessible from Online Report > the Log tab by clicking on the chart icon under additional details:

The load-time for the individual aspects of each webpage-element is displayed within the waterfall chart, including: Domain Name Server (DNS) resolution time, Connection, SSL, Request, First packet, Download, Start Time, End Time and Speed (in bytes per second (bps), and kilobytes per second (kbps)).

waterfall_chart

A Waterfall Chart data are updated automatically after each playback of a UserView script in the EveryStep Scripting Tool.

Find more details in the video walkthrough of Waterfall Chart.