A port is sort of a generic term for an "opening into the computer". They work in different ways but mostly they are for connecting peripherals into the computer.
As wikipedia says:
Computer port (hardware)
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Ports on the Apple iBook (Early 2003)
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Ports on the Apple iBook (Early 2003)
In computer hardware, a port serves as an interface between the computer and other computers or devices in the form of an electrically wired outlet on a piece of equipment into which a plug or cable connects. These hardware ports have different physical shapes such as male, female, round, rectangular, square, oblong, etc. There is some standardization to physical properties and function. For instance, most computers have a keyboard port (currently round, or telephone type), into which the keyboard is connected.
Hardware ports can almost always be divided into two groups:
* Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-).
* Parallel ports send multiple bits at the same time over several sets of wires.
The system bus that holds circuit cards for a computer "Mother Board (MO)" is a form of parallel port. Note that light fiber, microwave, and other technologies (i.e. quantum) may have special cases.
Hardware port trunking (HPT) is a technology that allows multiple hardware ports to be aggregated into a single group, effectively creating a single connection with a higher bandwidth. This technology also provides a higher degree of fault tolerance. Compare this to Software Port Trunking (SPT) where two agents (websites, channels, etc.) are bonded into one with the same effectiveness, i.e. ISDN B1 (64K) plus B2 (64K) equals data throughput of 128K.
These are hardware ports, there are also software ports that allow computers to connect to eachother (TCP/IP etc)
http://en.wikipedia.org/wiki/Computer_port_%28software%29
http://en.wikipedia.org/wiki/Computer_port_%28hardware%29