The word "颔联" is formed by combining the character "颔", which here metaphorically denotes the second position in a sequence akin to a chin's place below the head, with "联", meaning a couplet or paired lines in poetry. It specifically refers to the third and fourth lines of an eight-line regulated verse poem, constituting the second couplet that typically elaborates on the theme introduced by the first couplet. This term derives from a conventional analogy in Chinese poetics that assigns body-part metaphors to couplets based on their order and function within the poem's structure.