This question and answer comes from the Sound Devices website (Tech Notes). It is a great resource, and we encourage everyone to visit their site and dig through all the information.

Q: The 7-Series recorders have two options for WAV files, WAV mono and WAV poly. What’s the difference between these two WAV file types?

A: When choosing WAV mono (monophonic) as your file type the 7-Series will generate separate data files for each individual track recorded. The mono files generated by the 7-Series recorders have file names similar to T01_1.WAV and T01_2.WAV. The _1 and _2 after the take numbers are the mono designators added to the file name. These represent individual tracks.
When choosing WAV poly (polyphonic) as your file type the 7-Series will generate one data file containing multiple tracks. The poly files generated by the 7-Series have file names similar to T01.WAV, no matter how many tracks are contained within the file.
Note: Wave Agent, the Sound Devices file conversion utility for Windows-based computers, will convert WAV files between monophonic and polyphonic formats.