A virtual keyboard is an app that works like a keyboard, but appears onscreen, that you type into with the mouse.
This On-Screen Keyboard is a virtual keyboard that you can install on a USB drive, and run it one any PC you happen to be using.
The keyboard itself is not particularly attractive, but functional. You can resize it to suite you, which is good, and it remembers your settings when you exit. This type of keyboard protects you against hardware keyloggers, but not against keylogging software - so it doesn't protect you from malicious programs that try to save your entered passwords and so on.
This doesn't do more than the on screen keyboard built into Windows, but it dows mean that you can take your settings anywhere with you, if it's something you use regularly..
Virtual keyboards are a niche product, but On-Screen Keyboard Portable is a perfectly good on, although it has no special features.