In vexillology, the canton is a rectangular emblem at the top left of a flag. The canton can also be a flag itself. For example, Australia has the Union Jack as their canton.
The flag of the Republic of China (Taiwan) has a navy blue canton bearing a white sun with 12 triangular rays. (This flag's canton is also used as the Taiwanese naval jack and the Kuomintang's party flag.)
The flag of Togo has a red canton bearing a white five-pointed star.
The flag of Tonga has a white canton bearing a red Greek cross couped.
The flag of Tuvalu features the Union Flag in its canton.
The flag of the United States has 50 white five-pointed stars on a blue canton (a.k.a. union), standing for the country's 50 states (This flag's canton is also used as United States Naval Jack/Jack of the United States).