The prefix 'tera' is used to denote a trillion, which is a number equal to 1, 000, 000, 000, 000. It is derived from the Greek word 'teras', meaning monster or marvel. The prefix is often used in scientific notation to denote large numbers, such as in the fields of physics and chemistry. In everyday life, it is used to describe very large numbers, such as the national debt or the world population.