USD/JPY is the paring of the US dollar against the Japanese yen.
It shows you how many Japanese yen you would need to purchase 1 US dollar. The first currency in the pair is the base currency – so in this case it would be USD. JPY is the second currency, so it is the quote currency.
For example, if the price for USD/JPY is at 113.18 this means it would cost 113.18JPY to purchase 1USD.