noun
1.
a. : a set of linguistic forms (as verb forms, pronouns, and inflectional affixes) referring to someone or something that is neither the speaker or writer of the utterance in which they occur nor the one to whom that utterance is addressed
Latin videt “he sees” is in the third person singular
English they is a nominative plural pronoun of the third person
b. : a linguistic form belonging to such a set
English is and goes are third person
2. : reference of a linguistic form to someone or something that is neither the speaker or writer of the utterance in which it occurs nor the one to whom that utterance is addressed
the Latin verb ending -t that marks the third person