One of the most prevalent connection ports on today’s computers and peripheral devices is Universal Serial Bus (USB), and you can recognize a USB port or cable by its distinctive rectangular male or female end. The current version of USB is 2.0; previous versions are not compatible. If your desktop or laptop is a fairly new Macintosh, then you will have USB ports. Older Macs probably have something different. Windows machines switched to USB ports earlier than Macs, but some older PCs still have non-USB ports.
One of the most common non-USB ports is the serial port. This kind of cable-port combination routinely has pins of varying numbers on cables that fit in corresponding numbers of holes in ports. Even some of the most recently manufactured computers have serial ports for connecting peripherals like printers and scanners.
A problem can arise if you buy a newer computer and want to connect it to an older printer. The computer likely has a USB port, but the printer probably has a serial port. This can be the case with newer computers as well. In order to connect the two devices, you need a USB adapter.
The USB adapter connects USB-port devices to non-USB-port devices. It usually has a USB cable on one end and a non-USB cable on the other end. Just plug the correct end into the correct port, and you can overcome what would seem to be an insurmountable problem. The adapter solves that problem for you.
Another common kind of USB adapter these days is one that connects an iPod or other MP3 player to its power charger. A portable music player will likely have not a USB port, but rather some kind of serial port. This is where the adapter comes in handy. The cable that comes with the music player will have the serial cable on one end and a USB cable on the other end. The charger device that connects to an electrical outlet will have a USB port, into which you can plug the charging cable in order to juice up the music player. In this case, the charging device itself is the adapter.
You can also find a USB adapter that works with wireless devices. A keyboard, mouse, or headset can be connected to your computer using a dongle that plugs into a USB port on the computer but doesn’t need to connect to anything on the other side. This might not sound like the same sort of device as the ones described above, but it is a USB adapter in that it connects a USB port with a non-USB-port device.