This is the 7508th most frequent Spanish word.
isaac
"Isaac" is a proper noun, a given name, and does not have a specific definition in Spanish beyond referring to the biblical or personal name.
In this sentence, 'Isaac' is a proper noun referring to a person's name.
Isaac es un nombre común en varios países.
Isaac is a common name in several countries.
Here, 'Isaac' again acts as a proper noun, identifying the individual who wrote the book.
El libro que Isaac escribió ganó un premio.
The book that Isaac wrote won an award.
In this use, 'Isaac' indicates a specific person characterized by certain qualities.