The usage of the word "gap"" specifically refers to the positive difference between exports and imports, i.e.
US active trade balance of the U.S. after World War II, which led to the difference between the need for dollars and their limited supply.
The result was the risk of a slowdown in foreign trade, which depended on the convertibility of European currencies into US dollars.
The Bretton Woods monetary system was a key dollar service used in international transactions.
This shortcoming was addressed by creating dollars and paying them to other states, which was also one of the goals of the Marshall Plan.