“Ta.” Is a Quick, Casual “Thanks”

In Australia, ta can stand on its own as “thank you”. It is brief, friendly and casual, and is often heard when someone hands over change, holds a door or does a small everyday favour.

A: Here’s your change.
B: Ta.

It is not a universal substitute for thank you. In a formal email, after significant help, or whenever you want the gratitude to carry more weight, thank you is the better choice. Ta is also used in British English but is uncommon in the United States; an unfamiliar listener may hear it as a name or an abbreviation.

https://www.abc.net.au/education/learn-english/learn-english-weird-and-wonderful-aussie-slang-terms/8036750
https://dictionary.cambridge.org/dictionary/english/ta