What line is a thin line interrupted by a z-shaped symbol?

It is difficult to tell without the context but it could be a "broken" axis in a chart. That is an axis which starts from a value other than zero.

For example, if you wanted a chart where the horizontal axis covered recent years, you would normally not want the axis to go back to 0. So you would have a z-flash on the x-axis and start at a convenient year, say 1990.