Virtual Studio Technology (VST)
Definition - What does Virtual Studio Technology (VST) mean?
Techopedia explains Virtual Studio Technology (VST)
There are many types of VST plugins, which can be mostly classified as instruments (VSTi) or effects. VSTi does exactly what its name implies, as it emulates different musical instruments so that the recording engineer or musician does not need to procure the specific instrument or find someone who can play it. Modern VST plugins provide their own custom GUI, but older ones tended to rely on the UI of the host software.