"Mō dǐ" literally means 'to feel the bottom' — combining 摸 (mō, 'to touch or feel') and 底 (dǐ, 'bottom' or 'foundation'). Figuratively, it refers to conducting a thorough preliminary investigation or assessment to understand the current situation, baseline conditions, or underlying facts before making decisions or taking action. It emphasizes gathering foundational knowledge, often in an exploratory, diagnostic, or evaluative way.

The term is widely used in professional, educational, and administrative contexts — for example, teachers may 摸底 students’ prior knowledge before starting a new unit; doctors may 摸底 a patient’s medical history before diagnosis; or officials may 摸底 public opinion before policy rollout. While originally metaphorical, it functions almost exclusively as a verb and rarely appears as a noun without modification (e.g., 摸底工作, 'investigation work'). It carries a neutral-to-formal register and implies methodical, often official or systematic inquiry.