Final answer:
A cairn is a human-made pile or stack of stones that serves as a grave marker or other memorial. Cairns have been part of human history since ancient times and appear in various cultures worldwide.
Step-by-step explanation:
An explanation of this term includes the understanding that a cairn is a human-made pile or stack of stones often used as grave markers but also utilized for a variety of other purposes such as landmarks and memorials. Cairns have been used since ancient times across various cultures. In contrast, a menhir is a single upright standing stone, a dolmen consists of two or more vertical megaliths supporting a large flat horizontal capstone (usually employed as a tomb), and a henge refers to a circular prehistoric earthwork, which can include stone or wooden circles like Stonehenge.
Crucial to archaeological studies, cairns are found in various places in the world. Especially noteworthy is their appearance in Neolithic sites, where they signify the burial places of prominent individuals or mark significant territories. They are found in a variety of settings, from the mountainsides of Scotland to the plains of South America, where they serve as both a memorial to the deceased and a waypoint for travelers.