AHJ — Authority Having Jurisdiction

The body or individual responsible for enforcing the code on a given project — typically the municipal building department, the fire department, or a provincial authority. The AHJ decides which edition of a standard applies and whether your documentation passes. Note that in Ontario the Fire Code itself sets the personnel qualification for testing, inspection and alteration work (Division C, Article 1.2.1.2) — the AHJ enforces it rather than defining it.