GarageBand '11: region
Regions are the building blocks of a project. Each time you record an instrument or drag a loop to the timeline, you create a region that contains the music you recorded, or the music in the loop.
Regions appear as rounded rectangles in the timeline. There are several different types of regions, which are different colors in the timeline.
Real Instrument regions from your recordings are purple. Real Instrument regions from Apple Loops are blue.
Software Instrument regions from recordings, loops, and imported MIDI files are green.
Regions from imported audio files are orange.
You can select regions in the timeline and edit them in a variety of ways, including copying and pasting, looping, resizing, splitting and joining, transposing, and renaming them.