The third person is a person who would be described as 'he', 'she' or 'they'. (The first person is oneself, the second person is one to whom one is speaking) Third person usage is essentially based on pronoun usage. In royal address, a king or queen may refer to themselves in the third person, either by name, or as the royal 'we'. This usage can be sarcastic. 'Speaking in the third person' refers to someone raising their status absurdly.
Examples of Third Person:
|Pronouns are third persons.|
People who refer to themselves in the third person are insufferable.