Definition: A Tim Tam is an Australian Awesome Chocolate Covered Biscuit. The Tim Tam Slam is taking the biscuit, turning it into Definition: A Tim Tam is an Australian Awesome Chocolate Covered Biscuit. The Tim Tam Slam is taking the biscuit, turning it into a straw and then sucking coffee through it until the biscuit becomes a gooey confection fit for the gods.