The prefixes TERA and TREGA are both used to denote the number one trillion. TERA is derived from the Greek word 'teras' meaning 'MONSTER' and is used in the International System of Units (SI) to represent one trillion. TREGA is derived from the Latin word 'trigintillion' and is used in the long scale system of naming numbers to represent one trillion. Both terms are used to refer to the same number, one trillion.