What does this definition of "hinterland" mean?

I came across the word "hinterland" on Merriam-Webster a few hours ago. I looked up this word on Dictionary.com. Here is what it gave me.

Source Dictionary.com

1) Often hinterlands. the remote or less developed parts of a country; back country:

2) The hinterlands are usually much more picturesque than the urban areas.

3) the land lying behind a coastal region.

4) an area or sphere of influence in the unoccupied interior claimed by the state possessing the coast.

5) an inland area supplying goods, especially trade goods, to a port.

I understand all the meanings except for the fifth definition, the one about "an inland area supplying goods, especially trade goods, to a port" I checked Cambridge Dictionary to seek further clarification but this online dictionary's entry doesn't really shed much light on the matter.

Source Cambridge Dictionary

ECONOMICS

• the area that surrounds a big city or port and on which the city or port depends for economic growth:
  Example: China is Hong Kong's economic hinterland and biggest trading partner.

I explored other websites to see what I could dig up to clear away the fog of the enigmatic fifth definition that befuddles my mind

Source Wikipedia "

• Originally the term was associated with the area of a port in which materials for export and import are stored and shipped. In shipping usage, a port's hinterland is the area that it serves, both for imports and for exports."

Source Briticannica.com "

• An export hinterland is the backcountry region from which the goods being shipped from the port originate and an import hinterland is the backcountry region for which the goods shipped to the port are destined. Export and import hinterlands have complementary forelands that lie on the seaward side of the port. An export foreland is the region to which the goods being shipped from the port are bound and an import foreland is the region from which goods being shipped to the port originate."

These are the only conclusions that I was able to come up with: 1) a non-coastal area/region that acts as a major logistics hub with two functions of 1) receiving and storing imported goods from a nearby coastal port/town and 2) shipping locally produced goods to the same nearby port for export; and 2) a regional/urban place that is closely linked economically with a nearby town or city in the sense that this place supplies goods to shore up the economy of the urban port/town? I may be wrong, so I'm asking professionals for a second opinion.