Port and Port Forwarding

A port is a physical or virtual connection which ranges from 1 till 655355 (integer values) on which a device or service operates on a computer.

a physical port is different from a virtual port although they have similar properties on running a service.

a physical port can be anything ranging from connection of a device to a serial port (com port), parallel port (Lpt1, Printer port), USB Universal Serial Bus port, Firewire (IEEE1394), P/S2 Port, VGA port, DVI port, HDMI port, minijack Port, Optical Port, LAN Port, IDE (PATA) ports, Serial Ata (SATA) and the like.

most peripherals run on these above mentioned such as Hard disks, CD/DVD roms, Mouse, Keyboards, etc

a Virtual port is a port which runs on a service on the internet.
Ports between 1 - 1024 are whats called private ports which are dedicated for very specific functions and work.
E.G.
1) FTP - 21
2) HTTP - 80
3) POP3 - 110
4) SMTP - 25

Remaining ports are open ports or random ports that can be used by some 3rd party applications or common applications.
E.G.

1) Remote Desktop (Terminal Services)- 3389
2) MS SQL - 1433
3) HTTP Proxy - 8080
4) HTTP alt - 8008

some open ports which are not defined by default can be used to mask a server in the internet or network so that only persons with the specific knowledge will know how to access the server.

Port Forwarding is what allows an external connection (client from office) to connect to the internal connection (host at home [behind firewall or router]) to access information by various methods,
1) Remote Desktop
2) HTTP
3) Virtual Private Network
4) Gaming Application