Classifying quadratic forms and their corresponding symmetrical matrices

Question

In my textbook it is written that a quadratic form $$Q(x) = x^{T}Ax$$is positive definite if and only if the eigenvalues of the symmetrical matrix A are all positive, negative definite if and only if the eigenvalues are all negative and indefintie if the eigenvalues are both negative and positive. Is there any connection to the eigenvalues of the matrix A if the quadratic form is positive semidefinite or negative semidefinite?