Focus is an abstract function defined in terms of the informational status of the constituent in question within the discourse. It may, but need not be expressed in accentual prominence, and if it is, the relationship between Focus and Accent need not to be one-to-one.
- Dik (1989), a pag.390

The pragmatic function of Focus pertains to the focality dimension of discourse. The focal information in a linguistic expression is that information which is relatively the most important or salient in the given communicative setting, and considered by S [Speaker] to be most essential for A [Addressee] to integrate into his pragmatic information.
- Dik (1989), a pag.277

When constituents which contain focal information behave in special ways on account of their focality, these constituents will be assigned the pragmatic function Focus; this function may be divided into different sub-functions [...]. Cross-linguistically speaking, the Focus function may manifest itself through one or more of the following focalizing devices: (i) prosodic prominence: emphatic accent; (ii) special constituent order: special position for Focus constituents in the linear order of the clause; (iii) special Focus markers: particles which mark off the Focus constituent from the rest of the clause. (iv) special Focus constructions: constructions which intrinsically define a specific constituent as having the Focus function.
- Dik (1989), a pag.278