Terra cotta - earth and fire, or fired earth. Terracotta is the commonest form of naturally occurring clay. If you find a deposit of clay while digging in a garden or field, or chunks falling from a cliff, then chances are this is what you have. As clay in the ground it can be grey, yellow, brown or red. But it contains iron in one form or another, and when fired that iron oxidises (think rust) and gives the warm orange colour that is mostly associated with flowerpots, house bricks and roof tiles.
Terracotta is a form of earthenware. It is fired at low temperature - typically 1000-1100C. It is porous, absorbing water, which is useful for flowerpots and not so good when you leave the pot outside in a frost. The absorbed water expands and the pots shatter. Terracotta has strong associations with places where frosts are rare, like mediterranean coastlines. The water absorption can be used to keep the contents of a pot cold - the constant surface evaporation having a cooling effect. It can also be used to filter water, catching a vast proportion of bacteria and viruses.
The best terracotta is a deep burnt orange, shows the marks of being thrown on the wheel. A scrape where it was cut free, the rough base smoothed over with a finger, the throwing rings and, if you are lucky, the finger- or thumbprint of a long-dead potter.
Terracotta turns up routinely on archeological digs, traded by the Romans all over Europe. When you create, handle and buy handmade terracotta pots you are participating in history, in an exchange that has continued for thousands of years.