A port, in networking, is a number that defines what application an internet connection is attempting to connect to.
Port numbers are typically well defined. For example, by definition, a mail server will “listen” for incoming connections on port 25. When an attempt is made to connect to that server requesting a connection to port 25, that means that the machine requesting the connection wants to “talk to” the email server listening there, presumably in order to send mail.
There are hundreds of different pre-defined port numbers for all common services. Some common examples:
* http is port 80 and https is 443
* Sending mail (SMTP) is typically port 25 and receiving mail (POP3) is port 110
* ftp, or file transfer protocol, uses both ports 21 and 22.
One way of looking at port numbers might be to think of them as apartment numbers in a large apartment building.
The apartment building’s street address might be analogous to the server’s IP address, which locates the apartment building (server). Once at the front door, the apartment number (port number) locates the specific resident (service) you wish to talk to. If that resident (service) doesn’t respond, it might be because their door is locked (access blocked, perhaps by a firewall) or they’re not home (the service isn’t running).
Not all port numbers exist on all servers, because not all servers provide all possible services; that would be analogous to an apartment number that doesn’t exist at a particular address.
Port, when used in reference to hardware, is a physical connection to a machine.
A desktop computer might come with several ports, including USB ports, networking ports, display ports, and more.
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manchester and Duluth; these access the sea via rivers or canals. Because of their roles as ports of entry for immigrants as well as soldiers in wartime, many port cities have experienced dramatic multi-ethnic and multicultural changes throughout their respective histories.
Ports are extremely important to the global economy; 70% of global merchandise trade by value passes through a port. For this reason, ports are also often densely populated settlements that provide the labor for processing and handling goods and related services for the ports. Today by far the greatest growth in port development is in Asia, the continent with some of the world's largest and busiest ports, such as Singapore and the Chinese ports of Shanghai and Ningbo-Zhoushan. As of 2020, the busiest passenger port in the world is the Port of Helsinki in Finland. Nevertheless, countless smaller ports do exist that may only serve their local tourism or fishing industries.
Ports can have a wide environmental impact on local ecologies and waterways, most importantly water quality, which can be caused by dredging, spills and other pollution. Ports are heavily affected by changing environmental factors caused by climate change as most port infrastructure is extremely vulnerable to sea level rise and coastal flooding. Internationally, global ports are beginning to identify ways to improve coastal management practices and integrate climate change adaptation practices into their construction.