Having no money right now, or very little. It is informal and friendly — the kind of thing you say to a friend, not on a form. The key idea is that it is temporary: you are strapped this week because you paid your rent, not because you are poor forever. Very often people say the longer phrase strapped for cash, and that phrase is more common than strapped alone. You can also be strapped for other things you have run out of: strapped for time, strapped for space, strapped for staff. Note that this word has a completely separate everyday meaning too — strapped means tied down with a strap, as in "the boxes were strapped to the roof of the car" — but the money meaning is the one here, and English speakers tell them apart by the situation, not by the word.