SFG
Noun
Meaning
(electronics, countable) Initialism of signal-flow graph.
(spectroscopy) Initialism of sum frequency generation.
Source: en.wiktionary.orgExamples
His grammatical descriptions go by the name of systemic functional grammar (SFG).
Thus, SFG does not describe language as a finite rule system, but rather as a system, realised by instantiations, that is continuously expanded by the very instantiations that realise it and that is continuously reproduced and recreated with use.