While polynomials are also basic PDFs, they convey mathematically a more special class of functions.

zfit.pdf.Bernstein(obs, coeffs[, ...])	Linear combination of Bernstein polynomials of order len(coeffs) - 1, the coeffs are overall scaling factors.
zfit.pdf.Chebyshev(obs, coeffs[, ...])	Linear combination of Chebyshev (first kind) polynomials of order len(coeffs), coeffs are scaling factors.
zfit.pdf.Legendre(obs, coeffs[, ...])	Linear combination of Legendre polynomials of order len(coeffs), the coeffs are overall scaling factors.
zfit.pdf.Chebyshev2(obs, coeffs[, ...])	Linear combination of Chebyshev (second kind) polynomials of order len(coeffs), coeffs are scaling factors.
zfit.pdf.Hermite(obs, coeffs[, ...])	Linear combination of Hermite polynomials (for physics) of order len(coeffs), with coeffs as scaling factors.
zfit.pdf.Laguerre(obs, coeffs[, ...])	Linear combination of Laguerre polynomials of order len(coeffs), the coeffs are overall scaling factors.
zfit.pdf.RecursivePolynomial(obs, coeffs[, ...])	1D polynomial generated via three-term recurrence.