A plug-in is a piece of music software that is inside a Digital Audio Workstation (DAW) such as Logic Pro. Many plug-ins come already installed as part of the sequencing program. However, one can create their own original plug-in and install it in the DAW system. Plug-ins come in a variety of formats. If you are going to buy or upload a separate plug-in, be sure it is compatible with your computer software system.