That's the proportional grid. You can use the Layer Menu or the Alt/Option + ' key to turn it on or off. The Ctrl/Cmnd + ' key turns the Grid on and off. By default the Grid is about 80 pixels and the proportional grid is 8 X 6 lines in a standard HD comp.
You can open Preferences using Alt/Option + Ctrl/Cmnd + ; and go to the Grids and Guides section to edit both of the grids.