If you do a "Google" search for flat white coffee, you will find a lot of information about it.
Here is a little bit of what I found:
Flat White
A flat white is similar to a latte and is mostly served in Australia and New Zealand. The drink is prepared, like a latte, with espresso and milk. The main difference between a latte and a flat white is the ratio of milk and espresso.
The flat white has less milk than a latte and usually a bit less foam on top. Unlike many people think, the flat white does have foam on top. Foaming milk whilst steaming gives the milk a creamier flavor so it’s recommended to always foam the milk, even when it’s just a little bit.
Be prepared to be served a latte without foam when ordering a flat white in most places.
According to some people a flat white should be made with milk just off boiling. However, be aware that the taste of milk changes above certain temperatures and therefore the recommended temperature is around 60 to 70 degrees Celsius.