This is the 7694th most frequent Japanese word.
博久
"博久" is a Japanese given name meaning "extensive knowledge and long-lasting."
Here, '博久' is used as a proper noun, indicating the name of a person.
博久は学校で先生をしています。
Hirohisa is a teacher at the school.
In this sentence, '博久' is used to explicitly state the name of an individual.
彼の名前は博久です。
His name is Hirohisa.
The word '博久' is used as a polite reference to an individual, with 'さん' indicating respect.