The terms VST and VSTi are often used interchangeably, but there is a difference between the two.

VST stands for "Virtual Studio Technology," which is a plugin interface developed by Steinberg for integrating software synthesizers and effects with digital audio workstations (DAWs). VST plugins can be used to simulate the sounds of traditional instruments or create unique sounds and effects.

VSTi, on the other hand, stands for "Virtual Studio Technology Instrument." This term is used specifically for plugins that are software synthesizers or samplers that generate sound when you play notes on a MIDI keyboard or other MIDI controller. In other words, VSTi plugins are designed to function as virtual instruments within your DAW.

So, while all VST plugins can be used as effects processors, not all VST plugins can function as virtual instruments. VSTi plugins, however, are specifically designed to function as virtual instruments and generate sounds in response to MIDI input.

Now you know the difference between VST and VSTi.