What is a 'plugin' used for in music software?

A plugin in music software serves as an additional feature or effect that enhances the software's functionality. It allows users to extend the capabilities of their digital audio workstation (DAW) or other music production software by incorporating new sounds, effects, or instruments. This can include virtual synthesizers, audio effects like reverb or compression, and various other tools that contribute to the creative process.

The flexibility offered by plugins enables musicians and producers to customize their setups and explore a wider range of sounds and effects, making them essential for professional music production. This versatility is why the correct answer highlights the additive nature of plugins in contrast to core functionalities or predetermined tools found within the software.