VST Plugins

VST (Virtual Studio Technology) is a plugin interface standard for connecting audio synthesizers and effects to sequencers, audio editors, etc. VST and similar standards allow traditional hardware synths and effects to be replaced with software.

VST plugins are software modules of which there are two kinds - VST instruments and VST effects. The VST plugin standard was created by Steinberg to allow third party developers to create plugins for use in VST hosts. The standard is cross platform, and is available on both Windows and Mac platforms.

VST instruments, otherwise known as VST synths or VSTis, generate sound in response to MIDI input - typically from a sequencer or keyboard. VST instruments fall into two main categories; samplers - which play back recorded sounds, and synthesizers - which generate sound mathematically. Some instruments, such as Alchemy blur the boundaries between sampling and synthesis, by allowing you to analyse samples and then re-synthesise them.

VST effects process incoming audio to produce an altered output. There are many kinds of effects, including distortion, compression, reverb, delay and filters.

Steinberg - creator of the VST standard
KvR Audio - VST resource - community site with forums, reviews, annoucements and database of freeware and commercial plugins
Wikipedia (VST plugins) - wiki entry with information on VST plugins