In which kind of book can you record your thoughts?

Explanation

A diary is mostly used privately for a person to write notes on his or her day, thoughts, or actions. It can also be more public, for instance in the shape of a webblog (blog), i.e. an online diary. Such a blog can be written by one person only and still be mainly private, or by a team of bloggers, and be used in a more professional context - such as experts describing their latest research for the benefit of readers. Diaries can also be used for studies or projects, giving an informal account of how a given study has run.