Definition:Irreducible (Representation Theory)

Definition

Linear Representation

Let $\rho: G \to \operatorname{GL} \left({V}\right)$ be a linear representation.

Then $\rho$ is irreducible if and only if it is not reducible.

That is, if and only if there exists no non-trivial proper vector subspace $W$ of $V$ such that:

$\forall g \in G: \rho \left({g}\right) \left({W}\right) \subseteq W$

G-Module

A $G$-module is irreducible if and only if the corresponding linear representation is irreducible.