This is the 6374th most frequent Spanish word.
bertrand
The word "bertrand" is not a Spanish word; it is typically a proper noun, such as a name.
In this sentence, 'Bertrand' is used as a proper noun, referring to a person's name.
Bertrand es mi amigo de la escuela.
Bertrand is my friend from school.
Here, 'Bertrand' is again a proper noun, used to identify the author of a book.
El libro escrito por Bertrand es muy interesante.
The book written by Bertrand is very interesting.
In this case, 'Bertrand' represents an individual's name whose intellectual work is of interest.