"Mask holder" and "mask extender" usually refer to a small strip that has a button at each end. Wear it to eliminate pressure or irritation behind the ears. It shows at the back of the head where the ear loops of the mask hook around the buttons instead of the ears. Another term is "ear saver". "Mask chains" and "mask lanyards" drape around the neck like necklaces. It's the same idea as wearing a badge holder, or a chain for reading glasses.