An SND (SouND) file is a digital sound file format. There is more than one.
Most commonly a .snd file contains a NeXT sound file. This is essentially the same as the au file format used by Sun Microsystems. The first four bytes of a .snd file contains the hex number 0x2e736e64 which displays as ".snd" when interpreted as ASCII text.
Another .snd file format is attributed to Apple Inc. Data stored in such files are commands for the Macintosh Sound Manager including 'wavetable' sample-based instruments and sound samples. Thus it is some kind of improved midi format. As well it can serve as a purely audio file format if only one command and one sound sample is stored in it. In this format, the first two bytes specify a 16-bit integer containing the number 1 or 2.
Programs supporting audio files with the .snd extension generally assume, and check, that it is NeXT/SUN (AU) format.
The manufacturer of electronic music instruments Akai had an audio file format with the extension .snd. The first byte contains the number 1 and the second the number 4.
The manufacturer of the HOM-BOT Robot Vacuum Cleaner LG Group is using audio files with the extension .snd. The sounds are encoded in PCM (single channel, 16 kHz, 16 bits signed).
The Unity Game Engine uses a compressed format called .snd for sound packages.