This is the 65th most frequent Icelandic word.
hvað
"What."
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 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'.