Demotic Greek (language of the people) is the modern vernacular form of the Greek language, and refers particularly to the form of the language that evolved naturally from ancient Greek, in opposition to the artificially archaic Katharevousa, which was the official standard until 1976. The two complemented each other in a typical example of diglossia, or the existence of two forms of a language (usually a "high" and a "low") employed by the same speaker depending on the social context, until the resolution of the Greek language question in favor of Demotic.
Demotic is often thought to be the same as the modern Greek language, but these two terms are not completely synonymous. While Demotic is a term applied to the naturally evolved colloquial language of the Greeks, the modern Greek language of today is more like a fusion of Demotic and Katharevousa; it can be viewed as a variety of Demotic which has been enriched by "educated" elements. Therefore, it is not wrong to call the spoken language of today Demotic, though such a terminology ignores the fact that modern Greek contains - especially in a written or official form - numerous words, grammatical forms and phonetical features that did not exist in colloquial speech and only entered the language through its archaic variety. Additionally, even the most archaic forms of Katharevousa were never thought of as ancient Greek, but were always called "modern Greek," so that the phrase "modern Greek" applies to Demotic, Standard Modern Greek and even Katharevousa.