Excess of an admissible Steenrod sequence ($e(I)=i_1-i_2-\cdots -i_r$)

The excess measures the minimum degree on which an admissible Steenrod monomial can be nonzero. Strict excess below $n$ picks out polynomial generators in the mod-two cohomology of $K(\mathbb{Z}/2,n)$; equality can correspond to a square, rather than a new generator.