# Cannot understand sage polynomial factor notation

Hello, I am generating a random polynomial over the field GF(2^6), and when I print it, I cannot undertstand the values of certain factors:

The polynomial looks like this: x^9 + (z6^5 + z6^3)*x + z6^4 + z6^2 + z6 What do z6, z6^5 mean? I searched but I was unable to find an answer in the docs.