The discussion focuses on checking the invariance of terms in the Standard Model (SM) Lagrangian under the symmetries SU(3) x SU(2) x U(1). To verify gauge invariance, it is essential to ensure that each term in the Lagrangian is in the trivial representation of the SM gauge groups. If a term is in the trivial representation, it is considered gauge invariant; otherwise, it is not. This method provides a systematic approach to confirming the symmetry properties of the Lagrangian. Understanding these concepts is crucial for analyzing the underlying symmetries of the Standard Model.