What is meant by a meta-directing group? Give examples of it and explain the meta-directing effect of $-NO_2$.

(N/A) Definition: $A$ group attached to a benzene ring is called a meta-directing group if it directs the incoming electrophile to the meta-position during electrophilic aromatic substitution.
$(b)$ Examples: $-NO_2$,$-COOH$,$-SO_3H$,$-CHO$,$-COCH_3$,$-COCl$,$-COR$,$-COOR$ etc.,are meta-directing groups.
$(c)$ Meta-directing effect of $-NO_2$: The $-NO_2$ group is strongly electron-withdrawing due to its $-I$ and $-M$ effects. This withdraws electron density from the benzene ring,specifically from the ortho and para positions,creating a partial positive charge $(+\delta)$ at these positions. The meta position remains relatively more electron-rich compared to the ortho and para positions. Consequently,an incoming electrophile is directed to the meta position. The resonance structures $(I-V)$ and the hybrid structure $(VI)$ illustrate this electron deficiency at the ortho and para positions.