What is meant by activating groups? Explain with suitable examples.

(N/A) Definition: Groups that are attached to the benzene ring and increase the electron density of the ring,thereby making it more reactive towards electrophilic aromatic substitution compared to benzene,are known as activating groups.
Examples: Groups like $-OH$,$-OR$,$-NH_{2}$,$-NHR$,and $-NHCOR$ are strong activating groups. They are ortho-para directing.
Explanation: Activating groups donate their electron density towards the benzene ring through resonance ($+M$ effect) or inductive effect ($+I$ effect). This increases the electron density in the ring,which facilitates the attack of an electrophile.
For example,alkyl groups $(R-)$ donate electrons via the inductive effect ($+I$ effect),while groups with lone pairs donate electrons via resonance ($+M$ effect).
Note: While halogens ($-Cl$,$-Br$) are ortho-para directing,they are deactivating groups because their strong $-I$ effect outweighs their $+M$ effect.