This is the 10th most frequent Spanish word.
es
"Es" means "is" in English, used for third-person singular in the present tense of "to be."
The copula "es" is used here to indicate a profession by identifying two entities as being the same.
Ella es médica.
She is a doctor.
The verb "es" describes a particular quality of the subject, in this case referring to an inherent characteristic of the book.
Este libro es interesante.
This book is interesting.
Here, "es" establishes the date or time of an event, anchoring it temporally for the speaker.