Im dealing with a matrix that is [nxm] in size, with each column representing an eigenvector. the question on my hw states: Reorder the eigenvectors in a decreasing order based on the corresponding eigenvalue and normalize each vi such that ||vi|| = 1. all i want to know is what does ||vi|| mean?

||x|| = length of vector x, which is equal to the square of the dot product of x. A normalized vector is also known as a unit vector, in which the length is 1.