Gridlines are similar to stripes and appear on the gauge background when enabled, as shown by the following image:

The settings relevant to gauge axis gridlines are available trough the Gauge Areas > Axes > Gridlines tab. There are two types of gridlines - major and minor. The first ones are synchronized with the major ticks on the axis and the latter are synchronized with the minor ticks (if enabled). The following settings are available for axis gridlines:

Show Major - controls the visibility of major grid lines.

Major Stroke Style - controls the stroke of major grid lines.

Show Minor - controls the visibility of minor grid lines.

Minor Stroke Style - controls the stroke of minor grid lines.