At a basic level, marine terminals are places where ships , trains, and trucks all exchange cargo. The marine terminal functions like an exchange point for all cargo.
The exchange hub
Marine terminals are a gathering spot for trains, trucks, and ships. At this spot, all three meet to exchange the cargo they carry. Trains and trucks drop off cargo for ships and pick up cargo that came off a ship. Ships pick up cargo bound for far off destinations and drop off cargo from abroad. The terminal is the organizational hub that each of these entities relies on for efficient trade. The terminals organize cargo by destination, size, and weight as it arrives to facilitate efficient handling of cargo.
Part of a line or independent
Terminals are typically on land that is leased from a port authority. In general, ports do not operate marine terminals. They lease the land to operators who perform all the work of moving cargo. Generally, terminals are separate entities from port authorities.
Terminals are either owned by a line or are independent. For example, APM terminals are owned by Maersk, Everport is owned by Evergreen. Ports America and SSA Terminals are both independently owned. Terminals customers are steamship lines. A terminal may have several customers or they may only have one.
Throughput business model
Terminals charge a set rate to discharge cargo and deliver it to a trucker or rail or to load cargo from a truck or rail. The business model is based on moving cargo, and a large volume of cargo for their customers - the shipping lines (MSC, Maersk, Evergreen, ONE, Hapag Lloyd, Wan Hai, etc). This business model incentivizes terminals to keep their operation running as smoothly and efficiently as possible for their customers to gain more volume moving through the facility.