心里 (xīn lǐ) literally means 'inside the heart' and functions as a noun meaning 'in one’s heart/mind' — referring to inner thoughts, feelings, emotions, or unspoken intentions. Though 心 (xīn) means 'heart' and 里 (lǐ) means 'inside' or 'within,' together they form an abstract spatial metaphor for the internal mental-emotional realm, not a physical location. It emphasizes subjectivity, privacy, and sincerity — what someone truly feels or thinks, often contrasting with outward behavior.

This term is commonly used in expressions about hidden emotions ('心里很高兴' — 'happy inside'), suppressed reactions ('心里很生气但没表现出来' — 'angry inside but didn’t show it'), or personal convictions ('我心里很清楚' — 'I know clearly in my heart/mind'). It frequently appears after pronouns (e.g., 我心里, 他心里) or demonstratives (e.g., 这件事我心里有数), and rarely stands alone without a modifier.