Besides being the name of the Japanese currency, yen (a different yen) means a casual desire. You can have a yen for sushi, and if you're in Japan, you can pay for the sushi with the yen in your wallet.
Yen is a casual word––think of it like "hankering." If you have an easy time remembering rhymes, think "I sometimes have a yen, to go back home again." Sometimes yen can even work as a verb––you can yen for pancakes, or yen for truffles, or yen for a time when you yenned for things other than food.