USB stands for “Universal Serial Bus”
This is not to be confused with “USP”, which is a marketing term meaning “Unique Selling Proposition” and describes what might be a small, insignificant, difference between one product and a competing one.
USB is a type of connection that was designed to be suitable for connecting all types of external items (“peripherals”) to a computer.
USB ports (the “socket” part) are much smaller than the parallel and serial ports of earlier generations of computers. Also, you can connect a device with a USB cable without having to re-start the computer to get it to recognise the device you’ve just plugged in. This is called “hot plugging”.
The most common type of USB connection that connects peripherals to a computer is USB Type A. This is the familiar rectangular connection that will only fit one way up. We are now on the third generation of USB connections – each one being faster than the previous one. USB connections are “backwardly compatible”, meaning that if you connect a later generation device to an earlier generation port then everything will work – but at the lower speed of the earlier generation port or connector.
If you are connecting a mouse, keyboard, or printer, the speed of the USB connection doesn’t matter much. If you are connecting an external hard drive then the speed does matter. A new portable external drive will almost certainly have a USB3 connection, so connect it to a USB3 port on the computer if at all possible. You can tell if a port is USB3 as it will either be partly blue when you look directly at it or it will have “SS” (for “Super Speed”) written very close to the port.
Printers have traditionally been connected using a different plug at the printer end. This is a square plug with two edges chamfered off. Once again, the plug can only be inserted into its port one way. This type of connection is called USB Type B. Having said that, most people prefer to connect their printer wirelessly these days, so the USB connection is redundant.
Lots of new laptops now feature a new generation of USB connection called Type C. This is much smaller than Type A and can be connected either way up. You can buy an adaptor to connect a Type B plug into a Type C port. For that matter you can get all kinds of adaptors for changing one type of USB port or plug into another. Go to Amazon, for instance, and type “USB adaptors” into the search box.
The end of a USB cable that connects to the device might be much smaller than the end connecting to the computer. An older design of this was called “mini USB”. The current design is even smaller and is called “micro USB”. Once again, the cable can only be connected to the port one way up.
There is another type of USB connection – just for Apple devices such as iPhones. This is called the “lightning” connector and it is used instead of the mini USB and micro USB connection of non-Apple devices. The other end of a “lightning cable” features a standard Type A plug.
USB connections allow data to be transferred between devices, but they can also transfer power as well as data. 2.5 inch external hard drives, for instance, are powered by the USB connection as well as the data transfer taking place along the USB connection. There are also some devices (mini fans, for instance) that are connected via USB simply to power them – ie with no data transfer taking place. You can even get a USB-powered gizmo that keeps your coffee warm (if you don’t mind risking knocking your coffee over into your keyboard).
I hope this helps to clarify a rather confusing area. The confusion is mainly caused, of course, by the fact that things change and improve over time and the changeover is never neat with a cut-off date. We always have lots of “generations” in use at the same time. Plus ca change…
If you’d like to know more about this utterly fascinating (!) subject, then you could try https://www.techdim.com/usb-2-vs-usb-3-use-usb-3-0-rather-usb-2-0/