A track represents one channel, or a predetermined collection of simultaneous, inseparable channels (as is often the case with stereo audio). In the DAW's main window, tracks are usually represented as rows, whereas time is represented by columns. A track may hold multiple regions, but usually only one of those regions can be heard at a time. The multitrack capability of modern software-based DAWs is one of the reasons for their success. Although each individual track can play only one region at a time, the use of multiple tracks allows the DAW's outputted audio to contain a virtually unlimited number of simultaneous regions. The most powerful aspect of this is that audio does not have to be recorded simultaneously in order to be played back simultaneously; you could sing a duet with yourself, for example.