Answer:
This type of trade is called Arbitrage trading.
Step-by-step explanation:
Arbitrage trading a simultaneously selling and buying of financial instruments or entering into various transactions at the same time in at least two different market to make money through the exploitation of price differences.
In this case, because there is price differences between the borrowing market in Japan and deposit market in Australia, the trader can earn profit by borrowing in Japan in yen, converting the amount into AUD and deposit it in Australia to earn 4% per annum profit.
Such scenario exists as a result of market inefficiency. As more and more trader does the same trading, borrowing cost in Japan will be higher ( due to higher demand) and deposit cost in Australia will be lower ( due to higher supply). In the end, market will be efficient and such trading will not lead to any profit gained from price differences.