内心 literally means 'inside heart' and refers to a person’s inner emotional or psychological world—their private thoughts, feelings, beliefs, and moral compass that aren’t visible to others. It emphasizes the subjective, introspective realm rather than outward behavior or appearance. The character 内 means 'inside' or 'inner', while 心 means 'heart', used here metaphorically for the seat of emotion and consciousness, as in many Chinese expressions (e.g., 心情, 心思).

This noun is commonly used in reflective, literary, or psychological contexts—such as discussing personal growth, authenticity, or emotional honesty. It often appears in phrases like 内心深处 (deep in one’s inner self), 内心平静 (inner peace), or 内心挣扎 (inner conflict). Unlike more casual terms like 心里, 内心 carries a slightly formal, thoughtful, or even philosophical tone, suggesting depth and sincerity.