<operating system> The Unix software device that discards any data written to it and supplies zero bytes of data when read. /dev/null is occasionally useful in situations where a file is required but no relevant file exists.
For example, if a program produced lots of output for debugging purposes but that output was not required when the program was deployed in a production environment and writing it to a file would waste disk space then the output could be written to /dev/null.
The term is used for a notional "black hole" in any information space. For example, a message, might end, "Kudos to email@example.com, flames to /dev/null".
See bit bucket.