A vector is normalized if its norm is 1. A set of vectors $\set{u_1, \dots , u_k}$ orthogonal if $u_i^\top u_j = 0$ whenever $i \neq j$. A set of vectors is orthonormal if the set is orthogonal and each vector is normalized.
An orthonormal set of vectors is also an independent set. In other words, orthonormality is stronger than independence.