There is only one file type that uses the .NVM extension:
PlayStation 2 BIOS Configuration File
Configuration file created for PlayStation 2 BIOS used in game emulation; contains data, such as language and time zone, used to configure a PlayStation 2; automatically created when first running BIOS; should remain in the BIOS folder.
NOTE: BIOS are necessary in order to emulate a PlayStation2 on a PC. In order to use programs such as PSX2, you must transfer the BIOS folder from your own PS2 to your PC.
scphXXXXX.nvm - File appears like this with the 5 digit X's replaced by the version of your BIOS.
Updated: June 19, 2013