noun A measure of length given by "the square root of the squares." Denoted by ||⋅||2, the two-norm of a vector v→=<a1,a2,…,an> is ||v→||2=a12+a22+⋯+an2. The two norm of an m×m matrix A is defined by maxv→≠0→||Av→||2||v→||2 where v→ is an m-dimensional vector that is not the zero vector.