This is the 6th most frequent Tamil word.
அவர
"He" or "They" (respectful form).
Here, 'அவருடைய' is used as a possessive form to indicate ownership (his).
அவருடைய பெயர் ரவி.
His name is Ravi.
Here, 'அவரை' is used in the accusative case to refer to him (direct object of the verb).
நான் இன்று அவரை சந்தித்தேன்.
I met him today.
Here, 'அவர்கள்' is the plural form used to denote respect or as a pronoun for 'they' (subject of the sentence).