"Port" in the computer / networking world is very contextual.

For network related hardware, a port is simply someplace to connect a cable or device (RS-232 port, Ethernet Port ..)

In a software realm, port usually refers to a layer 4 address ... where to send the information contained in the layer three packet that was contained in the layer two frame.

At the transport layer, your primary data is contained in TCP or UDP packets. Once the information has made it up the stack that far, there has to be a label or address to tell the protocol stack what kind of data it is, so it can be directed to the correct process (Telnet, FTP, SSH ...), the port number is that address.

Well known port numbers are things like port 23 (telnet), 20+21 (for FTP), 53 (DNS), SSH (22) and so on.

So if someone asked you "What is a port?" it is appropriate to ask "for hardware or software (protocol stack, programming, firwewall, IDS ...)?"

Hardware port = somewhere to plug something in

Software port = (essentially) a layer 4 address (protocol address).

There is another meaning in the software-related realm: port also means to adapt code meant for one system to another system (like porting an application that works on a PC to work on an old PowerPC Mac, or an iPhone, or from one router type to another).

Hope this helps

Good Luck

Scott