In ancient Rome, a matrix was a female animal kept for breeding, or a plant (sometimes called a "parent plant" or "mother plant") whose seeds were used for producing other plants. In English the word has taken on many related meanings. Mathematicians use it for a rectangular organization of numbers or symbols that can be used to make various calculations; geologists use it for the soil or rock in which a fossil is discovered, like a baby in the womb. And matrix was a good choice as the name of the reality in which all humans find themselves living in a famous series of science-fiction films.