The velocity chart gives a high-level view of the amount of work (Y axis) over your iterations or date range (X axis). You can see right away if you are losing or gaining velocity and if your amount of work is stable over your iterations.
Insight's velocity chart is composed of two parts:
The blue bars represent the amount of work your team completed during an iteration or period of time. It gives you an objective measure on how much points got accepted during the iteration.
The planned bars are the amount of work that was scheduled before or on the first day of the iteration. This feature is only available when you filter by iteration, because it would not make a lot of sense on arbitrary date ranges.
The planned bars include points for stories that were not completed in the previous iteration, planned on the new iteration or added on the first day of the new iteration.
Note: This chart supports all filters.