In the previous USD/JPY example, between 2005 and 2006 the U.S. Federal Reserve was aggressively raising interest rates from 2.25% in January to 4.25%, an increase of 200 basis points. During that same time, the Bank of Japan sat on its hands and left interest rates at zero. Therefore, the spread between U.S. and Japanese interest rates grew from 2.25% (2.25% - 0%) to 4.25% (4.25% - 0%). This is what we call an expanding interest rate spread.
Let's say a trader has 1,000 USD on their trading account. A regular lot of '1' on MetaTrader 4 is equal to 100,000 currency units. As it is possible to trade mini and even micro lots with Admiral Markets, a deposit this size would allow a trader to open micro lots (0.01 of a single lot or 1,000 currency units) with no leverage put in place. However, as a trader would usually be looking for around 2% return per trade, it could only be equal to 20 USD.