the.com/flagstone

means A flat slab of stone, usually sedimentary rock like sandstone or slate, cut or split for paving floors, walks, and patios.

from From 'flag,' an old word for a slab of stone used for paving — itself borrowed from a Scandinavian source like Old Norse 'flaga,' meaning a slab or flat piece of stone or turf. It has no relation to the flag you wave; this flag was lying down long before any were run up a pole. 'Stone' was tacked on later simply to make the meaning unmistakable.