This is the 65th most frequent Icelandic word.
hvað
"What."
Here, 'hvað' is used to form a question asking for information about an unidentified object or concept.
Hvað er þetta?
What is this?
Here, 'hvað' is employed in a subordinate clause to express the object of the action 'I should say'.
Ég veit ekki hvað ég á að segja.
I don't know what I should say.
In this sentence, 'hvað' is used to inquire about an action someone is performing.