A dog ear head takes the two top corners of a square-topped picket and cuts each one off at 45 degrees, leaving a short flat shoulder in the middle. The result looks a little like a dog's folded ear, hence the name, and it is one of the two everyday picket tops in the trade alongside a pointed head, common on both picket fences and butted paling fences.
The cut is sized by how much timber comes off each corner, not by a head height the way a pointed or French Gothic head is. That clip size cannot exceed half the picket width. Push it past halfway and the two 45 degree cuts meet in the middle, which erases the flat top entirely and turns a dog ear into a plain pointed head, so CAD60 trims an oversized clip back to fit.
Dog ear is a quick, cheap head to cut compared with a pointed or French Gothic profile, since it is two straight saw cuts rather than a shaped router pass, which is part of why it is the default head style on so many treated pine paling fences around Australian suburbs.