Apple Logic Pro 8 Getting Started - Manual (Page 13)

Chapter 1 Starting Your Project and Importing Media Files 13
Adding Media Files
When you record or add MIDI or audio files (media, in other words) to the Arrange
window, narrow rectangles called regions appear—horizontally aligned on track lanes.
An audio region represents an underlying audio file (or a portion of it). This can be an
existing or new audio recording. A MIDI region represents an individual recording, or
take of MIDI data. Again, this can be an existing or new recording.
 You can only record, import, and play back MIDI regions on software instrument or
external MIDI tracks. MIDI regions actually contain MIDI events.
 You can only record, import, and play back audio regions on audio tracks. Audio
regions are simply placeholders or pointers to underlying audio files.
Audio region MIDI region