If someone wanted to change currencies in the past, they had to first convert their currencies into US dollars, and only then could they convert their dollars into the currency they desired.
The United States dollar was known as a "vehicle currency" because it was used as a medium of exchange in international transactions.
For example, if a person wanted to convert their British pound into Japanese yen, they would have to first convert their pound into US dollars, and then these dollars into yen.
Individuals can now avoid the process of converting their currencies into US dollars by simply converting them directly into their desired currency, thanks to the invention of currency crosses.
GBP/JPY, EUR/JPY, EUR/CHF, and EUR/GBP are some examples of crosses.