Disposable Soft Synth Interface (DSSI) is a virtual instrument (software synthesizer) plugin architecture for use by music sequencer applications.
DSSI is sometimes described as Linux Audio Developer's Simple Plugin API (LADSPA) for instruments.
LADSPA is an audio effects plugin architecture for filters, reverbs and other sound processing software tools, whereas DSSI was designed specifically for instrument plugins that generate sound from note events.
This is partly because DSSI was intended to be a lightweight addition to LADSPA that would require little extra effort from authors of LADSPA hosts and plugins to support, and partly to avoid distracting too much developer effort from the Generalized Music Plug-in Interface (GMPI) plug-in initiative (which has since stalled).
Perhaps as a partial consequence of this early offhand approach to publicity, the number of DSSI plugins available remains small.