潭 is a bound form (b.f.) meaning 'deep pool', 'pond', or 'pit' — it almost never appears alone in modern Chinese. You'll find it as a component in place names (e.g., 龙潭 Lóngtán) and in compounds like 潭水 (tánshuǐ, 'pool water') or 深潭 (shēntán, 'deep pool'). The topographical sense 'pit/depression' is less common but appears in geological or literary contexts.