Meaning of “diary” - Learner’s Dictionary

diary

noun [ C ] uk us /ˈdaɪəri/
MEETINGS

A2 a book containing spaces for all the days and months of the year, in which you write meetings and other things that you must remember:

According to my diary, I've got two meetings on Monday.
THOUGHTS

A2 a book in which you write each day about your personal thoughts and experiences:

She kept a diary of her trip to Egypt.

(Definition of “diary” from the Cambridge Learner’s Dictionary © Cambridge University Press)