A boolean function f on N variables is called evasive if its decision tree complexity is N, i.e., one must query *all* the variables (in worst case) in order to decide if f(X) = 1.
Suppose we have a polynomial $P$ in variables $X_1, \\ldots, X_n$ with coefficients from a field $F$, with total degree at most $d$. The polynomial $P$ is given in terms of some algebraic expression involving $X_1, \\ldots, X_n$.