A diary is a personal book where someone writes down their thoughts, feelings, and experiences from day to day. When you keep a diary, you're creating a private record of your life: what happened at school, how you felt about an argument with a friend, your excitement before a big game, or your worries about an upcoming test.

People have kept diaries for centuries. Anne Frank's diary, written while she hid from danger during World War II, became one of the most important historical documents ever published. Explorers like Lewis and Clark kept detailed diaries of their journey across America, and scientists often maintain research diaries to track their observations and ideas.

Some people write in their diaries every single night before bed, while others write only when something important happens or when they need to work through complicated feelings.

A diary differs from a journal, though people sometimes use the words interchangeably. A diary typically focuses on daily events and personal feelings, while a journal might include sketches, lists, goals, or more structured writing. Either way, both give you a place to think clearly, remember important moments, and understand yourself better as you grow and change.