headstone

n.

A stone that is used to mark a grave.

It is a permanent marker, normally carved from stone, placed over or next to the site of a burial in a cemetery or elsewhere.

Synonyms:

gravestone
tombstone

Originally, a tombstone was the stone lid of a stone coffin, or the coffin itself, and a gravestone was the stone slab that was laid over a grave. Now all three terms are also used for markers placed at the head of the grave.