X-bar theory

Etymology
X signifies an arbitrary lexical category; certain structures are represented by this letter and an overbar.

Noun

 * 1)  A theory that posits a common syntactic structure for different lexical categories. Each phrase (XP) is the projection of a head (X) and may optionally include a specifier (sister of X-bar, daughter of XP), adjuncts (sister and daughter of X-bar) and complements (sister of X, daughter of X-bar).

Translations

 * Chinese:
 * Mandarin: X槓理論, X階理論, X標槓理論
 * French: théorie X-barre
 * Russian: X-штрих-теория