The symbol (the lower case Greek letter tau) has many common uses in mathematics, as summarized in the following table.
1. is an alternate notation for the divisor function .
4. is used as an alternate notation for the golden ratio .
5. As a characteristic time for exponential decay or growth, i.e., .
The symbol also has a number of other different meanings in physics, for example the tau particle, tau neutrino, as a symbol for torque, etc.