The term Flemish itself has become ambiguous. Nowadays, it is used in at least five ways, depending on the context. These include:
An indication of Dutch written and spoken in Flanders including the Dutch standard language as well as the non-standardized dialects, including intermediate forms between vernacular dialects and the standard. Some linguists avoid the term Flemish in this context and prefer the designation Belgian-Dutch or South-Dutch
A synonym for the so-called intermediate language in Flanders region, the Tussentaal
MultiTree considers Flemish to include the four principal Dutch dialects in the Flemish region (Flanders): Brabantian, East Flemish, West Flemish and Limburgish as well as three other dialects.Glottolog considers Flemish to be a separate (regional) language, which includes the dialects of Antverpian (the dialect of the city of Antwerp), French Flemish, West Flemish, East Flemish and Limburgish. Ethnologue considers Limburgish and West Flemish to be separate (regional) languages.
Map showing the dialects spoken in the Benelux; many in Flanders speak in a distinct dialect, while also using Flemish tussentaal and Standard Dutch; in writing, the dialects are hardly used, while Flemish and Dutch are nearly identical in this regard
Dutch is the majority language in northern Belgium, being used in written language by three-fifths of the population of Belgium. It is one of the three national languages of Belgium, together with French and German, and is the only official language of the Flemish Region.
The various Dutch dialects spoken in Belgium contain a number of lexical and a good amount of grammatical features which distinguish them from the standard Dutch. Basic Dutch words can have a completely different meaning in Flemish or imply different context. As in the Netherlands, the pronunciation of Standard Dutch is affected by the native dialect of the speaker.
All Dutch dialect groups spoken in Belgium are spoken in adjacent areas of the Netherlands as well. East Flemish forms a continuum with both Brabantic and West Flemish. Standard Dutch is primarily based on the Hollandic dialect  (spoken in the Western provinces of the Netherlands) and to a lesser extent on Brabantian, which is the dominant dialect in Flanders, as well as in the south of the Netherlands.
The supra-regional, semi-standardized colloquial form (mesolect) of Dutch spoken in Belgium uses the vocabulary and the sound inventory of the Brabantic dialects. It is often called an "in-between-language" or "intermediate language," intermediate between dialects and standard Dutch. Despite its name, Brabantian is the dominant contributor to the Flemish Dutch tussentaal.
It is a relatively new phenomenon that has been gaining popularity during the past decades. Some linguists note that it seems to be undergoing a process of (limited) standardisation or that it is evolving into a koiné variety.
Tussentaal is slowly gaining popularity in Flanders because it is used a lot in television dramas and comedies. Often, middle-class characters in a television series will be speaking tussentaal, lower-class characters use the dialect of the location where the show is set, and upper-class characters will speak Standard Dutch. That has given tussentaal the status of normalcy in Flanders. It is slowly being accepted by the general population, but it has met with objections from writers and academics who argue that it dilutes the usage of Standard Dutch.Tussentaal is used in entertainment television but rarely in informative programmes (like the news), which normally use Standard Dutch.
The word Vlaams itself is derived from flâm,  an Ingaevones word, from the Germanic flauma (a cognate to the English flow and the Old German word flaum), which means 'flow or current'. The name Vlaanderen was formed from a stem flâm-, with a suffix -ðr- attached.
^Depending on the definition of "Flemish" in context. Brabantian is classified as a dialect of Dutch. It is spoken in the historical Duchy of Brabant, spanning the Belgian provinces of Antwerp, Flemish Brabant and Brussels that are part of the modern region of Flanders.
^Depending on the definition of "Flemish" in context. Limburgish is either classified as a dialect of Dutch or as a separate language altogether. It is spoken in the historical Duchy of Limburg and County of Loon, spanning the Belgian province of Limburg that is part of the modern region of Flanders.
^Rys, K. & J. Taeldeman (2007). Fonologische ingrediënten van Vlaamse tussentaal. In: D. Sandra, R. Rymenans, P. Cuvelier et al. (red.), Tussen taal, spelling en onderwijs. Essays bij het emeritaat van Frans Daems. Gent: Academia Press, 1-9, p.2.