'Yī mǎ píng chuān' literally means 'one horse, flat riverplain' — evoking an image of a vast, uninterrupted expanse where a horse could gallop freely without encountering hills, valleys, or obstacles. The four characters combine to form a vivid idiom: 一 (one) emphasizes singularity and continuity; 马 (horse) symbolizes unimpeded movement; 平 (flat) denotes levelness; and 川 (riverplain) refers to broad, open land shaped by rivers. Though it contains 马 (horse), the idiom is not about animals but about topography — specifically, expansive, perfectly level terrain.

This idiom is used both literally (to describe actual geography like the North China Plain) and figuratively (to suggest simplicity, ease, or lack of barriers). It often appears in descriptive writing, travel narratives, or metaphorical expressions about smooth progress — for example, describing a project proceeding 'yī mǎ píng chuān' implies no complications arose. Its tone is neutral to slightly literary, common in formal speech and writing but rare in casual conversation.