# What is the period of a cipher?

For the following explanation of RC4:

It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the period of the cipher is overwhelmingly likely to be greater than $10^{100}$."

What does it mean by the period of the cipher and greater than $10^{100}$?

I think the 10100 is a typo and should be $10^{100}$ as shown here