projection
projection
A meatus is an opening; therefor, it's a depression, not a projection.
projection
projection
is a depression
....opening?
A fissure is an opening or crack in the Earth's crust, typically where tectonic plates meet. It is not a projection or depression, but rather a narrow, long fracture in the ground.
"A crest is a projection or ridge, especially of bone; cresta"source: chacha.com
projection. The bumps of bone around your knees and elbows are almost all called condyles.
maniac is a serious type of depression the other is voices inside your head
A bowl-shaped depression at the head of a glacial valley is called a cirque or a corrie. It is typically formed by the erosion of a glacier.
I think you are referring to a method of locating a nut in a piece of sheet metal. A rivet head nut is a nut with has a small projection not much thicker than the sheet metal to which you intend to fit it. This projection fits through a pre made hole in the sheet metal, and the small projection is peened over (deformed by hammering) to fix the nut to the sheet.