This is the 14th most frequent Icelandic word.
það
"Það" means "it" or "that" in English.
The word 'það' is used here as a dummy pronoun, similar to 'it' in English, to discuss the state of the weather.
Það er kalt úti.
It is cold outside.
In this sentence, 'það' serves as a pronoun representing an object that is known or referred to.
Ég veit það.
I know it.
Here, 'það' is used in a clause to mean 'what', indicating something unspecified being talked about.