MARKED AND UNMARKED TERMS [Originating in the work of the Russian linguist Nikolay Trubetzkoy (1890–1938) in relation to pairs of phonemes]. Terms in LINGUISTICS which designate a contrasting pair, one possessing a special ‘mark’, the other neutral: in play/played, play is unmarked and neutral, and played has the mark -ed. Similarly, host is unmarked, but hostess is morphologically marked for femaleness. The mark is not necessarily visible or audible: in the pair horse/mare, horse is the more general, unmarked term, while mare is marked for femaleness. In the pair cow/bull, cow is unmarked, while bull is marked for maleness. The terms are sometimes extended to wider, typological characteristics of languages, and also to social situations, to distinguish between normal (unmarked) behaviour and a less common variant.
Source: MARKED AND UNMARKED TERMS - Encyclopedia.com
In syntax there are different kinds of markedness; e.g., sentence structure, verbs and their objects, pronouns, and more. Here's one example, structure:
Unmarked: Max swims.
Marked: Does Max swim?
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