National Replacement Character Set
The National Replacement Character Set (NRCS) was a feature supported by later models of Digital's (DEC) computer terminal systems, starting with the VT200 series in 1983. NRCS allowed individual characters from one character set to be replaced by one from another set, allowing the construction of different character sets on the fly.
Source: Wikipedia — National Replacement Character Set (CC BY-SA 4.0)