Ports and Terminals are the lifeblood of all nations as they serve as hubs concerning trade. In times of peace, such junctions sustain economies while, in times of war, these junctions can prove critical to wartime industry. Generally, ports and terminals allow for access to ocean-going routes (primary regarding trade though also serving military warships) though some may serve as major land-based hubs in the case of landlocked countries (ex: Afghanistan), providing access in reaching the rest of a country. In times of war, control of major ports and terminals is one factor sought by warplanners when attempting to achieve complete victory over an enemy.
The Major Ports and Terminals ranking is decided by the values presented in the CIA World Factbook.
Sources: CIA.gov, CIA World Factbook, wikipedia.com, public domain print and media sources and user contributions. Some values may be estimated when official sources are lacking.