nLab unirational variety

An algebraic variety $X$ over a field $k$ is unirational if there is a dominant rational map of varieties $f : P^n_k \dashrightarrow X$. The class of unirational varieties is a natural generalization of a class of rational varieties. Usually, it is much easier to decide if a variety is unirational or not, than it is to decide whether or not it is rational.