Computers come with a variety of ports for connecting peripheral devices (see above). Parallel and serial ports have been used virtually since the PC was invented and are still included for connecting printers etc.
PS/2 ports are generally included for connecting keyboard and mouse. USB (Universal Serial Bus) provides a single standard socket at the back of the PC to connect peripherals like printers, PDAs (Personal Digital Assistant or handheld computers), external CD writers, modems, digital cameras and scanners etc.
USB2 is much faster than ordinary USB but the peripheral device being connected to the port has to be designed for USB2 to take advantage of the increased speed.
IEEE 1394, (an Institute of Electrical and Electronics Engineers standard) otherwise known as "firewire", ports are generally used for digital video (DV) cameras to allow for fast data transfer and also for some external CD writers.
In telephone systems, port refers to the number of people that can be using voicemail facilities on traditional switchboards at the same time. For example a 4 port or and 8 port voicemail.