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?
In this sentence, 'hvað' is used to inquire about an action someone is performing.
Hvað ertu að gera?
What are you doing?
Here, 'hvað' is employed in a subordinate clause to express the object of the action 'I should say'.