The red-and-white symbol in the left-hand corner on Australian flag mean?

The red-and-white symbol in the left-hand corner on the Australian flag is the Union Jack. The Union Jack is a combination of the flags of England and Scotland, which were merged in 1606. The flag of Ireland was added to the Union Jack in 1801, after the Act of Union.

Australia used the British Union flag as its national flag until 1901 when the Commonwealth of Australia was established. The current Australian flag was adopted in 1954 and consists of the Union Jack in the canton (upper left corner), the Commonwealth Star of seven points (representing the six states and one territory of Australia) in the lower right quadrant, and the Southern Cross constellation (representing the five states of Australia, and the Northern Territory) in the lower left quadrant.