It refers to most species of Australian tarantulas. It's like calling African t's baboons or calling South American t's bird eaters, it really doesn't mean anything specific. They're called whistling spiders bacause they stridulate readily and it sounds somewhat like a whistle or more accurately, a hiss. Technically it's neither because they don't have lips or vocal chords. It's stridulation, which is the rubbing together of hair-like bristles causing sound.