This is the 30th most frequent Icelandic word.
allt
"Allt" means "everything" or "all" in English.
In this context, 'allt' again functions as a pronoun, emphasizing the entirety or total of actions or possibilities.
Ég ætla að gera allt sem ég get fyrir þig.
I'm going to do everything I can for you.
Here, 'allt' serves as a determiner accompanying 'þetta', enhancing the meaning to encompass the entirety of the referred matter.
Allt þetta er mjög áhugavert.
All this is very interesting.
Here, 'allt' is used as a pronoun meaning 'everything', referring to all things or conditions in general.