Unramified prime of an Artin representation (reviewed)

If $\rho:\Gal(\overline\Q/\Q)\to\GL_n(\C)$ is an Artin representation, a prime $p$ is unramified if it is not ramified.

Equivalently, a prime is unramified if the inertia subgroup for a prime above $p$ in the Artin field of $\rho$ is contained in the kernel of $\rho$.