This is the 907th most frequent Bulgarian word.
вътре
"Inside."
The word 'вътре' specifies the location of the book being inside the bag.
Книгата е вътре в чантата.
The book is inside the bag.
The word 'вътре' is used as an adverb to indicate movement into the interior of a room.
Влез вътре в стаята, моля.
Please, come inside the room.
In this sentence, 'вътре' has a figurative meaning, denoting something figuratively located inside a person's heart.