Basic shapes are fundamendal PDFs, with often well-known functional form. They are usually fully analytically implemented and often a thin wrapper around Distribution. Any missing shape can be easily wrapped using WrapDistribution.

zfit.pdf.Gauss(mu, sigma, obs[, extended, ...])	Gaussian or Normal distribution with a mean (mu) and a standartdeviation (sigma).
zfit.pdf.Exponential([lam, obs, extended, ...])	Exponential function exp(lambda * x).
zfit.pdf.CrystalBall(mu, sigma, alpha, n, obs, *)	Crystal Ball shaped PDF.
zfit.pdf.DoubleCB(mu, sigma, alphal, nl, ...)	Double-sided Crystal Ball shaped PDF.
zfit.pdf.Uniform(low, high, obs, *[, ...])	Uniform distribution which is constant between low, high and zero outside.
zfit.pdf.Cauchy(m, gamma, obs, *[, ...])	Non-relativistic Breit-Wigner (Cauchy) PDF representing the energy distribution of a decaying particle.
zfit.pdf.TruncatedGauss(mu, sigma, low, ...)	Gaussian distribution that is 0 outside of low, high.
zfit.pdf.Poisson([lam, obs, extended, norm, ...])	Poisson distribution, parametrized with an event rate parameter (lamb).