This is the 452nd most frequent Serbian word.
петар
"Петар" is a Serbian male given name, equivalent to "Peter" in English.
The word 'Петар' serves as the proper noun, the subject of the sentence.
Петар је јуче дошао у школу.
Petar came to school yesterday.
The word 'Петру' is the dative case form of the proper noun 'Петар', used to indicate the indirect object.
Рекао сам Петру да дође сутра.
I told Petar to come tomorrow.
The word 'Петра' is the accusative case form of the proper noun 'Петар', functioning as the direct object.