This is the 969th most frequent Icelandic word.
njáll
"Njáll" is an Icelandic male given name, derived from Old Norse, meaning "champion" or "protector."
'Njáll' is used here as a proper noun, referring to a specific individual's name.
Njáll er mjög duglegur bóndasonur.
Njáll is a very diligent farmer's son.
The word 'Njálu' is the genitive form of 'Njáll', used here as part of the title of the famous Icelandic saga.
Ég er að lesa Njálu, en hún er mjög fræg saga.
I am reading Njáls saga, as it is a very famous story.
Similar to the first example, 'Njáll' is used here as a proper noun indicating a person's name.