The .MOD file format is used by various digital camcorder models (I.E JVC Everio) to save their videos. These files are often accompanied by small .MOI files which contain the videos' time-stamp information.
The .MOD format uses MPEG2 encoding for the video (similar to a VOB file on a DVD or the M2TS files used on Sony hard drive camcorders) and Dolby Digital AC-3 encoding for the audio track; and if you simply wish to view the files on your computer, it is reportedly safe to rename the extension from .mod to .mpg or .avi.
The known camcorder models that use the .MOD format are:
JVC: GZ-MG30, GZ-MG70, GZ-MG37, GZ-MG77, GZ-MG505, GZ-MG130, GZ-MG155, GZ-MG255, GZ-MG555
Panasonic: SDR-S100, SDR-S150, SDR-S10, SDR-H18, SDR-H200, SDR-H40, SDR-H60, SDR-SW20