Cuba stands among the Original 51 Members of the United Nations, and among the oldest members of GATT
Background
The United Nations lists Cuba among the Original 51 Members of the Organization - that is, Cuba was an original Member of the United Nations, from its founding year. India, Haiti, Mexico and the United States are on the same list of original Members. The World Trade Organization's member information page for Cuba records that Cuba has been a member of the WTO since 1995, and a member of GATT since 1 January 1948. Cuba also appears on the WTO list of the 128 countries that had signed GATT by 1994, which makes Cuba one of the oldest participants in the post-war trading system.
In plain words
GATT General Agreement on Tariffs and Trade — The tariff-cutting agreement that governed world trade before the World Trade Organization replaced it.
Original 51 Members Original 51 Members — The states that took part in founding the United Nations and signed its Charter at the start.