The term 'Sigma Successor' is a reference to the Greek letter Sigma and its successor, the Greek letter TAU. Sigma is the eighteenth letter of the Greek alphabet, while TAU is the nineteenth letter. Sigma is often used in mathematics and science to represent summation, while TAU is used to represent time constants. In general, Sigma Successor refers to the idea that something is following on from something else, usually with an improvement or advancement.