This is the 504th most frequent Serbian word.
je
"Je" is the present tense third-person singular form of the verb "to be" in Serbian, meaning "is."
'je' is a copula used to link the subject 'Ovo' to its complement 'knjiga'.
Ovo je knjiga.
This is a book.
'je' is a verb functioning as the third person singular present tense of 'to be'.
On je lekar.
He is a doctor.
'je' is used as part of the question construction 'Je li...' indicating emphasis in forming yes/no questions.