A bone knob, set in a depression.
Many North American shetland ewes have these bone knobs, although they may not be visible at a glance.
These ewes look "polled", but they are not really polled unless they are carrying a poll gene.
If they carry two horn genes (pp), they are more properly called "hornless".
These bone knobs can usually be felt on top of the head, even if they are not visible.
