The Loop Bracket allows you to loop the playback in Edit Mode to help when scripting complex shows.
To loop a section of a track, first, set the playhead and playback the section you wish to loop.
Select the area in the waveform that you wish to loop, right click to select "Loop Selection"
Once you have applied the Loop a yellow Loop Bracket will be displayed in the wave form
To delete, simply right click click and select "Clear Loop"