In algebra, a Weyl module is a representation of a reductivealgebraic group, introduced by Carter and Lusztig (1974, 1974b) and named after Hermann Weyl. In characteristic 0 these representations are irreducible, but in positive characteristic they can be reducible, and their decomposition into irreducible components can be hard to determine.
Carter, Roger W.; Lusztig, G. (1974b), "On the modular representations of the general linear and symmetric groups", Proceedings of the Second International Conference on the Theory of Groups (Australian Nat. Univ., Canberra, 1973), Lecture Notes in Mathematics, vol. 372, Berlin, New York: Springer-Verlag, pp. 218–220, doi:10.1007/BFb0065172, ISBN978-3-540-06845-7, MR0369503