'岩层' (yán céng) literally combines 岩 (yán), meaning 'rock' or 'cliff', and 层 (céng), meaning 'layer' or 'stratum'. Together, it refers to a distinct horizontal layer of rock in the Earth's crust, formed over geological time through sedimentation, volcanic activity, or metamorphism. Geologists use this term to describe and classify rock units based on composition, age, and fossil content.

The word is common in earth science, geography, and environmental studies — for example, when discussing fossil preservation, groundwater flow, or earthquake risks. It appears in academic texts, field reports, museum exhibits, and science journalism. While not used in everyday conversation, learners may encounter it in textbooks, documentaries, or travel contexts involving mountains, canyons, or caves — places where rock layers are visibly exposed.