This is the 606th most frequent Bulgarian word.
стара
"Stara" means "old" (feminine form) in English.
The word "стара" (old) is used as an adjective here, describing the noun "книга" (book), indicating its age.
Това е стара книга.
This is an old book.
In this sentence, "стара" (old) is again an adjective, this time describing "къщата" (house), referring to its age or condition.
Къщата изглежда много стара.
The house looks very old.
The word "старата" (old or elderly) is used here as a definite form of the adjective, qualifying the noun "жена" (woman).