日记 (rì jì) literally means 'day record' — 日 (rì) means 'day' or 'sun', and 记 (jì) means 'to record' or 'to note down'. Together, they refer to a personal written record of daily experiences, thoughts, feelings, or observations, typically kept regularly over time. Unlike formal reports or journals intended for publication, a 日记 is usually private, reflective, and informal in style.

This word is commonly used in school assignments, language learning practice, and self-reflection routines. Students often write short 日记 entries as homework to practice writing skills and vocabulary. Adults may keep 日记 for mindfulness, memory preservation, or emotional processing. While digital apps are increasingly popular, the traditional handwritten 日记 remains culturally valued in Chinese-speaking communities for its intimacy and discipline.