Noun
a square matrix with all elements not on the main diagonal equal to zero
Source: WordNetFor a diagonal matrix, this is true only if each element of the main diagonal—that is, every eigenvalue of M—is positive. Source: Internet
More generally, if a degenerate geometric algebra is allowed, then the orthogonal matrix is replaced by a block matrix that is orthogonal in the nondegenerate block, and the diagonal matrix has zero-valued entries along the degenerate dimensions. Source: Internet
It is however not enough to consider the leading principal minors only, as is checked on the diagonal matrix with entries 0 and -1. Source: Internet