This is the 26th most frequent Bulgarian word.
ни
The Bulgarian word "ни" means "us" or "our" depending on context.
In this example, "ни" acts as a possessive pronoun, used to show possessive relation "our".
Сестра ни е лекар.
Our sister is a doctor.
In this sentence, "ни" is a personal pronoun in the dative case, used to indicate the indirect object "us".
Моля, изпратете ни вашите документи.
Please send us your documents.
Here, "ни" is again a personal pronoun but is used in the genitive case, indicating possession or a beneficiary "us".