In telecommunication, a standard test tone is a pure tone with a standardized level generally used for level alignment of single links and of links in tandem.
For standardized test signal levels and frequencies, see MIL-STD-188-100 for United States Department of Defense (DOD) use, and the Code of Federal Regulations Title 47, part 68 for other Government agencies.
References
Standard test tone Wikipedia(Text) CC BY-SA