RS-274D is the recommended standard for numerically controlled machines developed by the Electronic Industry Association in the early 1960's. The RS-274D revision was approved in February, 1980. These standards provide a basis for the writing of numeric control programs.
There are a number of historical sidelights to this standard, many having to do with the original use of punched paper tape as the only data interchange medium. The 64-character EIA-244 paper tape standard is now (thankfully) obsolete, and ASCII character bit patterns are now the standard representation. This old tape standard had specific characters used for 'searching' for specific lines (program blocks) on the tape, 'rewinding' the tape, etc. Occasionally this obsolete language is still used when referring to some cnc control tasks.
The full NIST Enhanced Machine Controller is nc programmed using a variant of the RS274D language to control motion and I/O. This variant is called RS276NGC because it was developed for the Next Generation Controller, a project of the National Center for Manufacturing Science. The version of RS274 used by EMC adheres closely to the publications of the NCMS wherever those publications produce an unambiguous set. In some cases reference to other implementations of RS274 had to be made by NIST.