This is the 14277th most frequent German word.
hierin
"Hierin" means "in this" or "herein" in English.
In this sentence, 'hierin' serves as an adverb meaning 'in this'. It indicates that what follows is contained or explained within the context just mentioned.
Hierin liegt der Schlüssel des Erfolgs.
Herein lies the key to success.
Here, 'hierin' is used to reference a specified document or situation, meaning 'in what has just been referred to', emphasizing its localized reference.
Er fand die Fehler hierin sehr offensichtlich.
He found the errors herein very obvious.
In this example, 'hierin' means 'in this aspect or context', pointing to what follows as a key element currently being discussed.