  For a family of weight functions that include the general Jacobi weight
functions as special cases, exact condition for the convergence of the Fourier
orthogonal series in the weighted $L^p$ space is given. The result is then used
to establish a Marcinkiewicz-Zygmund type inequality and to study weighted mean
convergence of various interpolating polynomials based on the zeros of the
corresponding orthogonal polynomials.
