1. A pyramid of rough stones, raised for a memorial or mark of some kind:
a. as a memorial of some event, or a sepulchral monument over the grave of some person of distinction. Hence, to add a stone to any one’s cairn.“Cairn, n.”. OED Online. September 2015. Oxford University Press.
b. as a boundary-mark, a landmark on a mountain top or some prominent point…
c. A mere pile of stones.