I remember one thread discussing how symbols in one area of study do not neccessarily stand for the same thing in other areas. It's tough to keep track of all the different meanings of different symbols, constants, and functions denoted by Greek letters. For example we learned that in number theory $\mu$ stands for the Mobius function, but in Physics it is the coefficient of friction. I found a wiki page which summarizes the different uses of Greek letters in math and science, and thought it is interesting enough to share. Here is the link:

Greek Letters in Math and Science

Summary:

Different uses of Greek letters