From the Greek stele, pillar.
A stela is a tall, narrow slab made of stone or wood, usually inscribed or carved in relief with names, laws, pictures, designs, or dedications for the dead. They were used throughout Ancient Egypt, the Near East, Greece, and even by the Ancient Chinese and Maya. Often they were used for funerary purposes, but also as boundary markers and commemorative purposes.
Hammurabi's Code and the Rosetta Stone are two very famous example of steles.