The label "Flemish" for the variants of Dutch spoken in Belgium is today generally deprecated. The official languages of the country (under article 4 of the constitution) are Dutch, French and German. The use of the description "Flemish" (particularly by francophones or people from the Netherlands) is generally taken to mean that the speaker is trying to imply that they speak badly or "just a dialect, not a proper language".
The range of Dutch spoken in Flanders and Brussels is quite wide; the geographical distribution is pretty much on a continuum across the border between Belgium and the Netherlands, where the forms of speech in Zeeuwsvlaanderen and Limburg are equally far from the "standard" language (i.e. the dialect of the Randstad), to say nothing of Frisian, which has officially been granted full "language" status. It is broadly impossible to isolate any particular linguistic forms as being used throughout Flanders which are not also in use in various parts of the Netherlands, other than in quite restricted domains, particularly legal and bureaucratic language which has perforce developed in tandem with French, because of the need for unnaturally close equivalence between terms in a single legal and administrative system that operates in both languages. Broadly speaking, the degree of difference between the Dutch spoken in Belgium and in the Netherlands is somewhat less than that between British and American English; the problems of mutual intelligibility are nowhere near as bad, even if Dutch TV feels it has to subtitle anybody who comes from more than 15 km away from Hilversum.
The use of the word as a generic adjective to describe things from Flanders has no such loaded connotations and can be used with reasonable security.