In mathematics, a rational variety is an algebraic variety, over a given field K, which is birationally equivalent to a projective space of some dimension over K. This means that its function field is isomorphic to K, {\displaystyle K,} the field of all rational functions for some set { U 1, …, U d } {\displaystyle \{U_{1},\dots,U_{d}\}} of indeterminates, where d is the dimension of the variety. Wikipedia