This is the 4846th most frequent Russian word.
иностранной
"Foreign."
The word is used as an adjective to describe the language being foreign.
Она изучает иностранной язык.
She studies a foreign language.
Here, the word describes the type of literature being foreign.
Курс иностранной литературы очень интересен.
The course in foreign literature is very interesting.
In this case, it describes the specialized field dealing with foreign philology.