Datebook notation is a system of organizing events and tasks in a calendar or diary. It involves assigning a code to each ENTRY, such as an EVENT or task, which can then be used to quickly identify the ENTRY. The two most common codes are ENTRY (5 letters) and EVENT (5 letters). ENTRY is used to denote a task or appointment, while EVENT is used to denote a special occasion or gathering. This system of notation allows for quick and easy organization of events and tasks, making it easier to keep track of them.