Dollar Volume is simply the number of shares traded multiplied by the price. It is an alternative version of volume designed to account for money flowing into and out of an asset on a particular day.
z is the offset. An offset of 1 is 1 bar ago.
The dollar volume of the current bar is the following.
C * V
The dollar volume from the previous bar is as follows.
C1 * V1
The dollar volume from 5 bars ago has a similar pattern.
C5 * V5
Read more about using the Dollar Volume on Investopedia.