Illustrated Glossary of Organic Chemistry

Directing group (director): In electrophilic aromatic substitution, a benzene ring substituent that influences benzene ring nucleophilicity and arenium ion stability, causing the incoming electrophile to favor attack at particular positions on the benzene ring.

			+		+
		Ortho isomer Minor product		Meta isomer Major product		Para isomer Minor product

Bromination of nitrobenzene via electrophilic aromatic substitution gives mostly the meta product, so the NO₂ group is a meta director.