The initials of Virtual Studio Technology. In broad terms, you have stuff in your computer that you don’t actually have in real life. It takes significantly less space than the actual physical instruments, keys, synths, drum machines, pads, etc, etc. As most of that comes in the form of files, you just throw it into your DAW and you’re good to go. Omedetou gozaimasu [congratulations!]. Now you have every imaginable sound at your fingertips.