Parts are small regions inside an audio or a midi track. Parts separate sections of the track visually and logically.
You may select to work with or without parts by using the "Part" button in the Track Manager, or by using the "P" key (for more, see Keyboard Shortcuts).
A ghost part is a mirror of an existing part. When that original part is altered, all ghost parts that reference the original part are also altered.
In Audio Tracks
Parts in audio tracks are represented with actual disk files (so if your audio track has 5 parts, there are 5 disk files). This separation allows you to:
Ghost parts refer to the same file (they have duplicated file handles) and therefore, once you manipulate a part, all its ghosts are automatically converted.
Because audio parts are single files, they can overlap.
In Midi Tracks
Parts in midi tracks are not different disk files, but they are only visually groupped. That means that a midi note can be outside a midi part. You can do pretty much the same functions discussed above for audio parts. The exceptions are:
Byzantine midi tracks cannot have parts.