The degree of a polynomial is the highest power of the variable in a polynomial expression. The degree of the zero polynomial is either left undefined or is defined to be negative (usually -1 or $-\infty$) . The zero polynomial is the only kind of polynomial that has an undefined degree. It has no non-zero terms, and so, strictly speaking, it has no degree either. Therefore, the degree of the zero polynomial is either undefined or set equal to -1.