This is the 45th most frequent Bulgarian word.
ги
The Bulgarian word "ги" means "them."
The pronoun 'ги' is used here as a personal object pronoun referring to 'the books'.
Те прочетоха книгите и ги обсъдиха подробно.
They read the books and discussed them in detail.
Here, 'ги' is a personal object pronoun substituting 'the toys' as the object of the action.
Деца, не разпилявайте играчките, трябва да ги приберете.
Children, do not scatter the toys, you need to put them away.
In this sentence, 'ги' functions as a personal object pronoun referencing 'the paintings'.