The Play Panel is comprised of 3 optional windows that allow you to review what you've just recorded or call up any older clips and stills that may be stored on your hard-drive or SD card.
They include the Play Viewer window which shows the name of the selected clip and a running counter (starting from zero on each clip and not matching the camera's timecode). A slider under the play button allows the alteration of the speed of the playback.
The File Browser window allows the selection of the clip you will play in the Play Viewer.
You also have access to a Vector and Wave monitor window as seen in the Rec Panel for monitoring the recorded video clip during playback.