a book in which you record your thoughts or feelings or what has happened each day

While in hiding, Anne Frank kept a diary. 安妮‧弗兰克在躲匿期间坚持写日记。

a book with a separate space or page for each day, in which you write down your future arrangements, meetings, etc.

Don't forget to write/enter the date of the meeting in your diary. 别忘了在日程簿上标出开会的日期。