Ochre is a term used to describe natural mineral pigments - commonly red (red ochre) and yellow (yellow ochre). This is related to yesterday's discussion because both are iron oxide minerals.
Red ochre is derived from hematite (Fe2O3) which is oxidized iron and rusty red in color (rust and hematite are essentially the same thing). The name hematite comes from αἷμα (haima) the Greek word for blood (same root as hemoglobin) because of the color.
Cultures around the world have used hematite to make red ochre pigment since the Paleolithic (Stone Age). Below is a red ochre (and carbon black) wisent (European bison) in Altamira Cave, Spain.