Rational representation
In mathematics, in the representation theory of algebraic groups, a linear representation of an algebraic group is said to be rational if, viewed as a map from the group to the general linear group, it is a rational map of algebraic varieties. Finite direct sums and products of rational representations are rational. A rational  module is a module that can be expressed as a sum (not necessarily direct) of rational representations. References
 
 Springer Online Reference Works: Rational Representation

Representation theory of algebraic groups